Chapter 12 - Magnetic Effects of Electric Current (Ncert Solutions)
Ultimate NCERT Solutions for Chapter 12 Magnetic Effects of Electric Current
Updated Solution 2024-2025 Updated Solution 2024-2025
NCERT Solutions for Class 10 Science, Chapter 12 Magnetic Effects of Electric Current (Question/Answers, Activity, Experiment’s & Projects)
Chapter 12 Magnetic Effects of Electric Current
Activity 12.1
- Take a straight thick copper wire and place it between the points X and Y in an electric circuit, as shown in Fig. 12.1. The wire XY is kept perpendicular to the plane of paper.
- Horizontally place a small compass near to this copper wire. See the position of its needle.
- Pass the current through the circuit by inserting the key into the plug.
- Observe the change in the position of the compass needle.
QUESTIONS AND ANSWERS BASED ON ACTIVITY 12.1
Q 1. What is the setup in Activity 12.1?
Ans 1: In this activity, a thick copper wire is placed between two points (X and Y) in an electric circuit. The wire is kept perpendicular to the plane of the paper. A small compass is placed nearby to observe its behavior when current flows through the wire.
Q 2. What is the purpose of placing the compass near the copper wire?
Ans 2: The compass is placed to observe how the magnetic field created by the electric current flowing through the copper wire affects the direction of the compass needle.
Q 3. What happens to the compass needle when the current flows through the copper wire?
Ans 3: When the current flows through the copper wire, the compass needle changes its direction. This happens because the electric current creates a magnetic field around the wire, which influences the compass needle.
Q 4. Why should the wire XY be kept perpendicular to the plane of the paper?
Ans 4: The wire XY needs to be kept perpendicular to the plane of the paper to ensure that the magnetic field generated by the current flows in a way that allows the compass needle to be clearly affected and show a noticeable change in direction.
Q 5. What does this activity demonstrate about the relationship between electricity and magnetism?
Ans 5: This activity demonstrates that an electric current passing through a wire produces a magnetic field around the wire. It shows the connection between electricity and magnetism, a principle known as electromagnetism.
Questions
Q 1. Why does a compass needle get deflected when brought near a bar magnet?
Ans 1: A compass needle gets deflected near a bar magnet because:
- Magnetic Field Interaction: A bar magnet produces a magnetic field around it.
- Force on Compass Needle: The magnetic field exerts a force on the compass needle, which is itself a small magnet.
- Needle Alignment: The compass needle aligns with the magnetic field lines of the bar magnet, causing it to deflect from its original north-south direction.
- Opposite Poles Attract: The north pole of the compass needle is attracted to the south pole of the bar magnet and vice versa, leading to the deflection.
Activity 12.2
- Fix a sheet of white paper on a drawing board using some adhesive material.
- Place a bar magnet in the center of it.
- Sprinkle some iron filings uniformly around the bar magnet (Fig. 12.2). A salt-sprinkler may be used for this purpose.
- Now tap the board gently.
- What do you observe?
Questions based on the activity
Q 1. What do you observe?
Ans 1:
1. Iron filings align in distinct patterns: After tapping the board gently, the iron filings will rearrange themselves to form a pattern of curved lines around the bar magnet.
2. Magnetic field lines visualization:
- These curved patterns represent the magnetic field lines of the bar magnet.
- The lines emerge from the north pole of the magnet and curve around to enter the south pole.
3. Field line properties:
- The lines are denser near the poles, indicating that the magnetic field is stronger in these regions.
- As you move farther from the poles, the density of lines decreases, indicating a weaker magnetic field.
This activity visually demonstrates the magnetic field of a bar magnet and how it interacts with materials like iron filings.
Q 2. What is the purpose of sprinkling iron filings around the bar magnet?
Ans 2: The iron filings help us visualize the magnetic field lines created by the bar magnet.
Q 3. Why do the iron filings arrange themselves in a specific pattern?
Ans 3: The iron filings align along the magnetic field lines of the bar magnet because they are attracted to the magnetic force, which is strongest along these lines.
Q 4. What can you learn about the magnetic field from the pattern of the iron filings?
Ans 4:
- The field lines are denser near the poles, indicating stronger magnetic force.
- The lines never cross each other, showing that the magnetic field has a definite direction at every point.
- The lines form closed loops, going from the north pole to the south pole outside the magnet and through the magnet back to the north pole.
Q 5. What happens if you replace the bar magnet with a weaker magnet?
Ans 5: The pattern of the iron filings will still form, but the alignment may be less distinct, and the field lines might appear fainter because the magnetic force is weaker.
Q 6. Why do you need to tap the board gently?
Ans 6: Tapping helps the iron filings move freely and settle into the positions that align with the magnetic field lines.
Q 7. Can you see the magnetic field directly?
Ans 7: No, the magnetic field is invisible, but its effect on the iron filings allows us to observe its shape and direction.
Q 8. What practical applications use the concept of magnetic fields?
Ans 8:
- Navigation: Compasses work on magnetic fields.
- Electricity generation: Magnetic fields are essential in generators and motors.
- Data storage: Hard drives and magnetic tapes use magnetic fields to store information.
Activity 12.3
- Take a small compass and a bar magnet.
- Place the magnet on a sheet of white paper fixed on a drawing board, using some adhesive material.
- Mark the boundary of the magnet.
- Place the compass near the north pole of the magnet. How does it behave? The south pole of the needle points towards the north pole of the magnet. The north pole of the compass is directed away from the north pole of the magnet.
- Mark the position of two ends of the needle.
- Now move the needle to a new position such that its south pole occupies the position previously occupied by its north pole.
- In this way, proceed step by step till you reach the south pole of the magnet as shown in Fig. 12.3.
- Join the points marked on the paper by a smooth curve. This curve represents a field line.
- Repeat the above procedure and draw as many lines as you can. You will get a pattern shown in Fig. 12.4. These lines represent the magnetic field around the magnet. These are known as magnetic field lines.
- Observe the deflection in the compass needle as you move it along a field line. The deflection increases as the needle is moved towards the poles.
Questions based on the activity
Q 1: What is the purpose of this activity?
Ans 1: The activity helps us understand and visualize the magnetic field lines around a bar magnet and how a compass behaves in the presence of a magnetic field.
Q 2: Why does the compass needle deflect near the magnet?
Ans 2: The compass needle is a tiny magnet. Its south pole is attracted to the north pole of the bar magnet, and its north pole is repelled by the bar magnet’s north pole. This interaction causes the needle to align with the magnetic field lines of the bar magnet.
Q 3: What do the field lines represent?
Ans 3: The field lines represent the direction and strength of the magnetic field around the bar magnet.
Q 4: How do you draw a magnetic field line?
Ans 4:
- Place the compass near the magnet’s north pole.
- Mark the position of the two ends of the needle.
- Move the compass so that the south pole of the needle moves to the point where the north pole was.
- Repeat the process step by step until you reach the magnet’s south pole.
- Join the marked points with a smooth curve to create a field line.
Q 5: What pattern do the magnetic field lines form?
Ans 5: The field lines curve around the bar magnet, going from the magnet’s north pole to its south pole outside the magnet and from south to north inside the magnet, forming closed loops.
Q 6: What happens to the compass deflection as you move closer to the poles?
Ans 6: The deflection of the compass needle increases as you move closer to the poles because the magnetic field is strongest near the poles of the magnet.
Q 7: Why are magnetic field lines important?
Ans 7: Magnetic field lines help us visualize the invisible magnetic field. They show the direction of the field at different points and help us understand how the magnetic force acts on other objects.
Activity 12.4
- Take a long straight copper wire, two or three cells of 1.5 V each, and a plug key. Connect all of them in series as shown in Fig. 12.5 (a).
- Place the straight wire parallel to and over a compass needle.
- Plug the key in the circuit.
- Observe the direction of deflection of the north pole of the needle. If the current flows from north to south, as shown in Fig. 12.5 (a), the north pole of the compass needle would move towards the east.
- Replace the cell connections in the circuit as shown in Fig. 12.5 (b). This would result in the change of the direction of current through the copper wire, that is, from south to north.
- Observe the change in the direction of deflection of the needle. You will see that now the needle moves in opposite direction, that is, towards the west [Fig. 12.5 (b)]. It means that the direction of magnetic field produced by the electric current is also reversed.
Questions based on the activity
Q 1: What materials are needed for this experiment?
Ans 1: You will need a long straight copper wire, two or three 1.5 V cells, a plug key, and a compass needle.
Q 2: How should the copper wire and compass needle be arranged?
Ans 2: The copper wire should be placed parallel to and over the compass needle.
Q 3: What happens to the compass needle when the current flows from north to south?
Ans 3: The north pole of the compass needle deflects towards the east.
Q 4: What happens when you reverse the current direction (from south to north)?
Ans 4: The north pole of the compass needle deflects in the opposite direction, towards the west.
Q 5: What does this experiment demonstrate about the relationship between electric current and magnetic fields?
Ans 5: It shows that an electric current produces a magnetic field, and the direction of this magnetic field depends on the direction of the current.
Q 6: Why does the needle change its direction when the current is reversed?
Ans 6: The magnetic field around the wire changes its direction when the current direction is reversed, causing the compass needle to deflect in the opposite direction.
Q 7: How can you use this experiment to determine the direction of the magnetic field?
Ans 7: By observing the deflection of the compass needle, you can identify the direction of the magnetic field. When current flows from north to south, the magnetic field causes the needle to deflect eastward, and vice versa.
Activity 12.5
- Take a battery (12 V), a variable resistance (or a rheostat), an ammeter (0–5 A), a plug key, connecting wires and a long straight thick copper wire.
- Insert the thick wire through the center, normal to the plane of a rectangular cardboard. Take care that the cardboard is fixed and does not slide up or down.
- Connect the copper wire vertically between the points X and Y, as shown in Fig. 12.6 (a), in series with the battery, a plug and key.
- Sprinkle some iron filings uniformly on the cardboard. (You may use a salt sprinkler for this purpose.)
- Keep the variable of the rheostat at a fixed position and note the current through the ammeter.
- Close the key so that a current flows through the wire. Ensure that the copper wire placed between the points X and Y remains vertically straight.
- Gently tap the cardboard a few times. Observe the pattern of the iron filings. You would find that the iron filings align themselves showing a pattern of concentric circles around the copper wire (Fig. 12.6).
- What do these concentric circles represent? They represent the magnetic field lines.
- How can the direction of the magnetic field be found? Place a compass at a point (say P) over a circle. Observe the direction of the needle. The direction of the north pole of the compass needle would give the direction of the field lines produced by the electric current through the straight wire at point P. Show the direction by an arrow.
- Does the direction of magnetic field lines get reversed if the direction of current through the straight copper wire is reversed? Check it.
Questions based on the activity
Q 1: What happens to the iron filings when you tap the cardboard while current flows through the copper wire?
Ans 1: The iron filings align themselves in concentric circles around the copper wire. These circles represent the magnetic field lines created by the electric current.
Q 2: What do the concentric circles formed by the iron filings indicate?
Ans 2: The concentric circles indicate the magnetic field around the straight copper wire. This field is generated by the flow of electric current through the wire.
Q 3: How can you find the direction of the magnetic field around the wire?
Ans 3: Place a compass at a point on one of the concentric circles. The direction in which the north pole of the compass needle points gives the direction of the magnetic field at that point.
Q 4: What happens to the direction of the magnetic field lines if the current’s direction in the wire is reversed?
Ans 4: The direction of the magnetic field lines also reverses if the current’s direction in the wire is reversed.
Q 5: Why is the copper wire placed vertically between points X and Y?
Ans 5: The copper wire is placed vertically to ensure the magnetic field pattern is symmetrical and easy to observe on the horizontal cardboard.
Q 6: What role does the rheostat play in this activity?
Ans 6: The rheostat helps control the amount of current flowing through the circuit. In this activity, it is set to a fixed position to maintain a steady current.
Q 7: Why is it important to tap the cardboard gently during the experiment?
Ans 7: Tapping the cardboard helps the iron filings move freely and align themselves along the magnetic field lines, making the pattern more visible.
Q 8: How does this experiment demonstrate the relationship between electricity and magnetism?
Ans 8: The experiment shows that an electric current flowing through a conductor produces a magnetic field around it. This is a practical demonstration of the link between electricity and magnetism.
Q 9: What safety precautions should you take during this activity?
Ans 9:
- Ensure all connections are secure to avoid short circuits.
- Handle the battery and wires carefully to avoid electric shocks.
- Avoid letting the cardboard or copper wire overheat.
Q 10: How can you increase the strength of the magnetic field around the copper wire?
Ans 10: You can increase the strength of the magnetic field by:
- Increasing the current flowing through the wire.
- Using a thicker or more conductive wire.
Questions
Q 1. Draw magnetic field lines around a bar magnet.
Ans 1:
Q 2. List the properties of magnetic field lines.
Ans 2: the properties of magnetic field lines:
1. Imaginary Representation:
- Magnetic field lines are not real but are a convenient way to visualize the magnetic field in a region.
2. Direction:
- Outside a magnet, magnetic field lines emerge from the north pole and merge into the south pole.
- Inside a magnet, the lines travel from the south pole to the north pole, forming closed loops.
3. Continuous Loops:
- Magnetic field lines always form continuous closed loops. They do not have a beginning or an end.
4. No Intersection:
- Magnetic field lines never intersect. If they did, it would imply two directions of the magnetic field at the same point, which is impossible.
5. Density and Strength:
- The density of magnetic field lines (i.e., how close they are to each other) represents the strength of the magnetic field.
- Closer lines indicate a stronger magnetic field, and farther apart lines indicate a weaker field.
6. Tangent Indicates Direction:
- The tangent to a magnetic field line at any point gives the direction of the magnetic field at that point.
7. Repulsion and Attraction:
- Magnetic field lines exhibit repulsion between similar poles and attraction between opposite poles.
8. Do Not Pass Through Conductors Freely:
- Magnetic field lines avoid passing through materials with high magnetic reluctance and prefer low reluctance materials, such as ferromagnetic substances.
Q 3. Why don’t two magnetic field lines intersect each other?
Ans 3: Two magnetic field lines do not intersect each other because if they did, it would imply that at the point of intersection, the magnetic field has two different directions simultaneously. This is physically impossible since the magnetic field at any given point in space has a unique direction and magnitude.
Explanation:
- Magnetic Field Definition: The magnetic field is represented by field lines, where the tangent at any point on the line gives the direction of the magnetic field at that point.
- Contradiction in Intersection: If two magnetic field lines intersected, there would be two tangents at the point of intersection, indicating two directions of the magnetic field at the same location, which contradicts the concept of a unique field direction.
- Physical Consistency: Magnetic fields are vector fields, and the vector at any point must have a well-defined direction and magnitude. Therefore, magnetic field lines cannot cross each other.
Chapter 12 – Magnetic Effects of Electric Current Class 10 Notes, Question/Answer, Activity & Projects
Updated Solution 2024-2025
This complete solution is prepared as per the latest syllabus of 2024-25. If you have any further queries, feel free to ask!
Activity 12.6
- Take a rectangular cardboard having two holes. Insert a circular coil having large number of turns through them, normal to the plane of the cardboard.
- Connect the ends of the coil in series with a battery, a key and a rheostat, as shown in Fig. 12.9.
- Sprinkle iron filings uniformly on the cardboard.
- Plug the key.
- Tap the cardboard gently a few times. Note the pattern of the iron filings that emerges on the cardboard
Questions based on the activity
Q 1: What is the purpose of this activity?
Ans 1: The activity demonstrates the magnetic field pattern created by a current-carrying circular coil. It helps us visualize how electric current generates a magnetic field.
Q 2: Why are iron filings sprinkled on the cardboard?
Ans 2: Iron filings align themselves along the magnetic field lines created by the circular coil. This alignment makes the magnetic field pattern visible.
Q 3: What happens when you tap the cardboard gently after plugging the key?
Ans 3: Tapping helps the iron filings settle into the pattern of magnetic field lines. This makes the magnetic field around the circular coil clear and easy to observe.
Q 4: What pattern do the iron filings form around the coil?
Ans 4: The filings form concentric circles near the coil and spread outward, showing the circular nature of the magnetic field lines around the current-carrying coil.
Q 5: Why is the coil connected to a battery and key?
Ans 5: The battery provides the electric current needed to create a magnetic field, and the key allows us to control when the current flows through the coil.
Q 6: How does increasing the current in the coil affect the magnetic field?
Ans 6: Increasing the current makes the magnetic field stronger, and the pattern of iron filings becomes more prominent.
Q 7: What happens if we use a coil with more turns?
Ans 7: A coil with more turns produces a stronger magnetic field because the magnetic effects of each turn add up.
Q 8: What does this activity teach us about the relationship between electricity and magnetism?
Ans 8: It shows that electricity and magnetism are interconnected. An electric current produces a magnetic field, illustrating the principle of electromagnetism.
Q 9: How does the rheostat help in this setup?
Ans 9: The rheostat controls the current flowing through the coil. By adjusting it, we can vary the strength of the magnetic field.
Q 10: What safety precautions should be taken during this activity?
Ans 10: Ensure the battery does not overheat, handle the iron filings carefully to avoid contact with the eyes, and disconnect the circuit when not in use to prevent short circuits.
Questions
Q 1. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Ans 1: To find the direction of the magnetic field produced by a current-carrying circular loop, we apply the right-hand rule:
1. Inside the Loop:
- Imagine holding the loop with your right hand such that your fingers curl in the direction of the current (clockwise in this case).
- Your thumb will point in the direction of the magnetic field inside the loop.
- Since the current is flowing clockwise, the magnetic field inside the loop will point upward (out of the plane of the table).
2. Outside the Loop:
- On the outside of the loop, the magnetic field will follow the opposite direction.
- To determine the direction, again curl your fingers in the direction of the current, and your thumb will point in the direction of the magnetic field outside the loop.
- For a clockwise current, the magnetic field outside the loop points downward (into the plane of the table).
Thus:
- Inside the loop, the magnetic field points upward (out of the table).
- Outside the loop, the magnetic field points downward (into the table).
Q 2. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Ans 2:
Magnetic field lines are parallel straight lines inside the solenoid. So, the magnetic field is uniform inside the solenoid.
Q 3. Choose the correct option.
The magnetic field inside a long straight solenoid-carrying current
(a). is zero.
(b). decreases as we move towards its end.
(c). increases as we move towards its end
(d). is the same at all points.
Ans 3: (b). decreases as we move towards its end.
Explanation: Inside a long, straight solenoid carrying a current, the magnetic field is relatively uniform and strong in the center. However, as you move toward the ends of the solenoid, the magnetic field decreases and becomes weaker. At the ends, the field lines spread out, causing a reduction in the field strength.
Activity 12.7
- Take a small aluminium rod AB (of about 5 cm). Using two connecting wires suspend it horizontally from a stand, as shown in Fig. 12.12.
- Place a strong horse-shoe magnet in such a way that the rod lies between the two poles with the magnetic field directed upwards. For this put the north pole of the magnet vertically below and south pole vertically above the aluminium rod (Fig. 12.12).
- Connect the aluminium rod in series with a battery, a key and a rheostat.
- Now pass a current through the aluminium rod from end B to end A.
- What do you observe? It is observed that the rod is displaced towards the left. You will notice that the rod gets displaced.
- Reverse the direction of current flowing through the rod and observe the direction of its displacement. It is now towards the right. Why does the rod get displaced?
Questions based on the activity
Q 1. What is the purpose of the experiment with the aluminium rod?
Ans 1: The purpose of the experiment is to observe the effect of a magnetic field on a current-carrying conductor (the aluminium rod) and understand how the direction of the current affects the force on the rod.
Q 2. What equipment is used in this experiment?
Ans 2: The equipment used in this experiment includes an aluminium rod, a horse-shoe magnet, connecting wires, a stand, a battery, a key, a rheostat, and the necessary components to complete the circuit.
Q 3. How is the rod suspended in the experiment?
Ans 3: The aluminium rod is suspended horizontally using two connecting wires attached to a stand. The rod is placed between the poles of a horse-shoe magnet.
Q 4. What is the role of the magnetic field in this experiment?
Ans 4: The magnetic field from the horse-shoe magnet interacts with the current flowing through the aluminium rod. The direction of the magnetic field is upward, which plays a key role in the displacement of the rod when current flows through it.
Q 5. What happens when the current flows through the aluminium rod from end B to end A?
Ans 5: When current flows from end B to end A, the aluminium rod moves towards the left. This happens because of the force exerted by the magnetic field on the current-carrying conductor, as explained by the Lorentz force.
Q 6. What happens when you reverse the direction of current?
Ans 6: When the direction of the current is reversed (i.e., from A to B), the displacement of the rod is now towards the right. This shows that the direction of the force is dependent on the direction of the current.
Q 7. Why does the rod get displaced when current flows through it?
Ans 7: The rod gets displaced due to the interaction between the magnetic field and the electric current. According to Fleming’s left-hand rule, the force on the rod is perpendicular to both the magnetic field and the direction of the current. The direction of the force changes based on the direction of the current.
Q 8. What principle can you explain using this activity?
Ans 8: This activity demonstrates the principle of the motor effect, which states that a current-carrying conductor placed in a magnetic field experiences a force. The direction of this force can be determined using Fleming’s left-hand rule.
Q 9. What is Fleming’s left-hand rule and how does it apply here?
Ans 9: Fleming’s left-hand rule states that if you hold the thumb, forefinger, and middle finger of your left hand perpendicular to each other, the thumb will point in the direction of the force, the forefinger will point in the direction of the magnetic field, and the middle finger will point in the direction of the current. In this experiment, the direction of displacement of the rod depends on the direction of the current and the magnetic field.
Q 10. Why does the direction of displacement change when the current direction is reversed?
Ans 10: When the current direction is reversed, the force acting on the rod also changes direction. This happens because the force is dependent on the direction of the current, so reversing the current changes the force, causing the rod to move in the opposite direction.
Questions
Q 1. Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass
(b) speed
(c) velocity
(d) momentum
Ans 1: The correct answers are:
(b) speed
(c) velocity
(d) momentum
Explanation:
- Speed: When a proton moves in a magnetic field, its speed can change. The magnetic force can cause the proton to accelerate, which can change its speed.
- Velocity: The velocity of the proton can change because velocity is a vector quantity (it includes both speed and direction). The magnetic force can change the direction of the proton’s motion, thus changing its velocity.
- Momentum: Since momentum is the product of mass and velocity, and velocity changes (due to the change in direction), the proton’s momentum can also change.
However, mass does not change when a proton moves in a magnetic field, so (a) is incorrect.
Q 2. In Activity 12.7, how do we think the displacement of rod AB will be affected if
(i) current in rod AB is increased;
(ii) a stronger horse-shoe magnet is used; and
(iii) length of the rod AB is increased?
Ans 2: In Activity 12.7, the displacement of the rod AB (which is typically part of a setup involving a magnetic field and current) is influenced by several factors:
1. If the current in rod AB is increased:
The displacement of rod AB will increase. This is because the force acting on the rod in the magnetic field is given by F = BIL, where:
- B is the magnetic field strength,
- I is the current,
- L is the length of the rod.
As the current increases, the force on the rod also increases, leading to a larger displacement.
2. If a stronger horse-shoe magnet is used:
The displacement of rod AB will also increase. The magnetic field strength B depends on the strength of the magnet. A stronger magnet produces a stronger magnetic field, which in turn increases the force acting on the rod. This results in a greater displacement.
3. If the length of the rod AB is increased:
The displacement of the rod will increase as well. The force on the rod is directly proportional to its length L. So, increasing the length of the rod increases the total force acting on it, leading to a greater displacement.
In summary, increasing the current, using a stronger magnet, or increasing the length of the rod will all lead to a larger displacement of the rod AB.
Q 3. A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south
(b) towards east
(c) downward
(d) upward
Ans 3: (b) towards east.
Explanation: According to the right-hand rule for the magnetic force, the force on a positively charged particle is given by the cross product of the velocity of the particle and the magnetic field. If the particle is moving towards the west (negative x-direction) and is deflected towards the north (positive y-direction), the magnetic field must be directed towards the east (positive z-direction) for the force to be in the northward direction.
Questions
Q 1. Name two safety measures commonly used in electric circuits and appliances.
Ans 1: Two common safety measures used in electric circuits and appliances are:
- Fuses or Circuit Breakers: These protect circuits from overloads and short circuits. If the current exceeds a safe level, the fuse blows or the circuit breaker trips, disconnecting the power and preventing damage or fire.
- Grounding (Earthing): This provides a safe path for electrical current to flow into the ground in case of a fault. It reduces the risk of electric shock and helps prevent electrical fires by ensuring that excess electricity is safely dissipated.
Q 2. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Ans 2: The electric oven has a power rating of 2 kW (2000 W), and it is connected to a domestic electric circuit with a voltage of 220 V and a current rating of 5 A.
To calculate the current required by the oven, we use the formula:
P = V × I
Where:
- P is the power (2000 W),
- V is the voltage (220 V),
- I is the current.
Rearranging the formula to solve for current:
I = P/V = 2000/220 ≈ 9.09 A
The oven requires approximately 9.09 A, but the circuit’s current rating is only 5 A. Since the required current exceeds the circuit’s rating, this could result in the circuit being overloaded, which may cause the circuit breaker to trip, or in severe cases, damage the wiring or cause a fire hazard.
Result: The oven cannot be safely operated on this circuit without potentially causing overloading and safety issues.
Q 3. What precaution should be taken to avoid the overloading of domestic electric circuits?
Ans 3: To avoid overloading domestic electric circuits, ensure the total electrical load does not exceed the circuit’s rated capacity. Use appliances with appropriate wattage, avoid using too many high-power devices on the same circuit, and install circuit breakers or fuses that can interrupt power in case of overloads. Regularly check for damaged wiring or faulty equipment and replace them as needed.
Exercise
Q 1. Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(c) The field consists of radial lines originating from the wire.
(d) The field consists of concentric circles centers on the wire.
Ans 1: (d) The field consists of concentric circles centered on the wire.
Explanation: The magnetic field around a long straight current-carrying wire forms concentric circles that are centered on the wire, with the direction of the field given by the right-hand rule.
Q 2. At the time of short circuit, the current in the circuit
(a) reduces substantially
(b) does not change.
(c) increases heavily
(d) vary continuously.
Ans 2: (c) increases heavily.
Explanation: During a short circuit, the resistance in the circuit drops drastically, causing the current to increase significantly as per Ohm’s law (I = V/R). This can lead to damage if not controlled.
Q 3. State whether the following statements are true or false.
(a) The field at the center of a long circular coil carrying current will be parallel straight lines.
Ans (a) False: The magnetic field at the center of a long circular coil carrying current is uniform and circular, not parallel straight lines.
(b) A wire with a green insulation is usually the live wire of an electric supply.
Ans (b) False: A wire with green insulation is usually the earth (ground) wire, not the live wire. The live wire is typically red or brown.
Q 4. List two methods of producing magnetic fields.
Ans 4: Two methods of producing magnetic fields are:
- Electric Current (Electromagnetic Method): A magnetic field is produced when an electric current flows through a conductor, such as a wire. This is the principle behind electromagnets, where a current in a coil of wire creates a magnetic field around it.
- Permanent Magnets: Certain materials, like iron, cobalt, and nickel, have intrinsic magnetic properties. When these materials are magnetized (usually through physical alignment of their atomic magnetic moments), they create a persistent magnetic field.
Q 5. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
Ans 5: The force experienced by a current-carrying conductor placed in a magnetic field is largest when the current flows perpendicular to the magnetic field. This is described by the equation: F = BIL sin(θ)
Where:
- F is the magnetic force
- B is the magnetic field strength
- I is the current
- L is the length of the conductor in the field
- Θ is the angle between the magnetic field and the current direction
When the current is perpendicular to the magnetic field (θ=90∘), the sine term (sin(θ)) equals 1, resulting in the maximum force.
Q 6. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
Ans 6: The direction of the magnetic field is into the page (or screen).
Explanation: According to the Lorentz force law, the force on a moving charged particle (like an electron) is given by the cross product of the velocity vector and the magnetic field vector: F = q(v × B).
- The electron beam is moving horizontally towards the front wall, so its velocity is directed horizontally.
- The force on the electron is to the right (as stated), which means the magnetic force is acting to the right side of the chamber.
Using the right-hand rule for the direction of the force on a negatively charged particle (like an electron), if the thumb points in the direction of the velocity (towards the front), and the force is directed to the right, then the magnetic field must be directed into the page to produce this rightward force.
Q 7. State the rule to determine the direction of a
(i) magnetic field produced around a straight conductor-carrying current,
(ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it,
(iii) current induced in a coil due to its rotation in a magnetic field.
Ans 7: Here are the rules for each of the scenarios:
(i) Magnetic field produced around a straight conductor carrying current:
- Rule: The direction of the magnetic field around a straight conductor is given by Ampère’s right-hand rule.
- Explanation: Point the thumb of your right hand in the direction of the current, and the curl of your fingers will show the direction of the magnetic field around the conductor.
(ii) Force experienced by a current-carrying straight conductor placed in a magnetic field:
- Rule: The direction of the force on a current-carrying conductor in a magnetic field is given by Fleming’s Left-Hand Rule.
- Explanation: Point the thumb, forefinger, and middle finger of your left hand perpendicular to each other. The thumb represents the direction of the force (motion), the forefinger represents the direction of the magnetic field, and the middle finger represents the direction of the current.
(iii) Current induced in a coil due to its rotation in a magnetic field:
- Rule: The direction of the induced current in a coil rotating in a magnetic field is determined by Fleming’s Right-Hand Rule.
- Explanation: Point the thumb of your right hand in the direction of motion of the conductor (coil), the index finger in the direction of the magnetic field, and the middle finger will point in the direction of the induced current.
Q 8. When does an electric short circuit occur?
Ans 8: An electric short circuit occurs when a low-resistance path is created in an electrical circuit, allowing current to flow along an unintended route. This typically happens when wires or components come into contact with each other, bypassing the intended load (like a light bulb or appliance). The sudden surge in current can cause overheating, damage to electrical components, or even fires. Short circuits are often caused by faulty wiring, damaged insulation, or a malfunction in the electrical system.
Q 9. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Ans 9: The function of an earth wire is to provide a safe path for electric current to flow into the ground in case of a fault, such as a short circuit or leakage of current from a metallic appliance. This prevents the appliance from becoming live, which could result in electric shocks or fires.
It is necessary to earth metallic appliances to protect users from electrical hazards. If a fault occurs, the earth wire directs the current away from the appliance and into the ground, minimizing the risk of electric shock.
Chapter 12– Magnetic Effects of Electric Current Class 10 Notes, Question/Answer, Activity & Projects
Updated Solution 2024-2025
This complete solution is prepared as per the latest syllabus of 2024-25. If you have any further queries, feel free to ask! 