Magnetic Effects of Electric Current Class 10 Competency Questions

20 Questions | 55 Marks

A group of students is setting up an experiment to demonstrate the magnetic effect of current. They have a straight copper wire, a battery, a key, and a compass. They place the compass near the wire and pass current through it.(a) What will the students observe when the current flows through the wire? [1 mark](b) If they reverse the direction of current, how will the observation change? [1 mark](c) Explain why this observation occurs, referring to the concept of magnetic fields. 2marks

A student is trying to draw magnetic field lines around a bar magnet using iron filings.(a) Describe the pattern they would observe on the cardboard when iron filings are sprinkled around the bar magnet. [1 mark](b) What do these iron filings represent? [1 mark](c) List any two properties of magnetic field lines that can be inferred from this pattern. 2marks

Assertion (A): Magnetic field lines never intersect each other.Reason (R): A compass needle points in a unique direction at any given point. 2marks

A long straight wire carries a current of 5 A. Calculate the magnetic field at a distance of 10 cm from the wire. (Given

μ_{0} = 4 π \times 10^{- 7}

T m/A) 3marks

Consider a circular coil of wire.(a) How does the magnetic field at the centre of the coil change if the current flowing through it is doubled? [1 mark](b) How does the magnetic field at the centre of the coil change if the number of turns in the coil is doubled, keeping the current the same? [1 mark](c) Name the rule used to determine the direction of the magnetic field produced by a current-carrying circular loop. 1mark

A solenoid is used to create a strong magnetic field.(a) Describe the pattern of the magnetic field lines inside the solenoid. [1 mark](b) What is the nature of the magnetic field inside the solenoid? [1 mark](c) How can this solenoid be used to make an electromagnet? 2marks

A current-carrying conductor is placed in a magnetic field.(a) State the rule that can be used to determine the direction of the force on the conductor. [1 mark](b) Under what condition is the force experienced by the conductor the maximum? 1mark

A proton enters a magnetic field with a velocity.Assertion (A): If the proton enters the magnetic field perpendicular to it, its velocity changes.Reason (R): A moving charge in a magnetic field experiences a force. 2marks

A group of students is investigating the direction of the magnetic field around a current-carrying straight wire. They use a compass.(a) Describe an activity to demonstrate the magnetic field pattern and its direction around a straight conductor carrying current. [3 marks](b) How does the magnetic field strength vary with the distance from the wire? 1mark

A 15 A fuse is used in a household circuit. The circuit supplies power to a television (200 W, 220 V) and a fan (100 W, 220 V).(a) Calculate the current drawn by the television and the fan individually. [2 marks](b) Calculate the total current drawn by both appliances when operating simultaneously. [1 mark](c) Will the fuse blow if both are operated together? Justify your answer. 2marks

Assertion (A): When an electron beam moves from back wall to front wall in a chamber and deflects to the right due to a magnetic field, the magnetic field is directed upwards.Reason (R): Fleming’s left-hand rule relates the direction of motion of charge, magnetic field, and the resulting force. 3marks

A copper wire is bent into a circular loop and a current flows through it.(a) Draw the magnetic field lines produced around this circular loop. [2 marks](b) What happens to the magnetic field strength at the centre of the loop if the current is increased? 1mark

A domestic electric circuit has a live wire, a neutral wire, and an earth wire.(a) What is the potential difference between the live wire and the neutral wire in India? [1 mark](b) What is the function of the earth wire, especially for appliances with metallic bodies? 2marks

A 2 kW electric heater is connected to a 220 V mains supply.(a) Calculate the current drawn by the heater. [2 marks](b) If a 5 A fuse is used, will it protect the circuit from overloading? Explain. 2marks

Assertion (A): A strong horse-shoe magnet is used to demonstrate the force on a current-carrying conductor.Reason (R): The magnetic field produced by the current-carrying conductor interacts with the external magnetic field, resulting in a force. 2marks

A student observes that an electron beam moving horizontally is deflected downwards by a magnetic field.(a) What is the direction of the current in the electron beam? [1 mark](b) Using Fleming’s left-hand rule, determine the direction of the magnetic field. 2marks

An electric motor utilizes the principle of the force on a current-carrying conductor in a magnetic field.(a) State the rule used to determine the direction of force on a current-carrying conductor. [1 mark](b) How does the magnitude of this force change if the length of the conductor in the magnetic field is increased? 1mark

A solenoid is used to magnetize a piece of soft iron.(a) What is the name of the magnet formed? [1 mark](b) List two factors that can be changed to increase the strength of this magnet. 2marks

Case Study: A homeowner is concerned about electrical safety in their house. They have a main fuse, individual circuit fuses, and all metallic appliances are earthed.(a) Why are separate circuits with different current ratings (e.g., 5A and 15A) used in a house? [2 marks](b) What happens during a short circuit, and how does a fuse protect the circuit? [2 marks](c) Explain the necessity of earthing metallic appliances. 1mark

Assertion (A): The magnetic field around a straight current-carrying wire is in the form of concentric circles.Reason (R): The right-hand thumb rule helps to determine the direction of the magnetic field around a straight current-carrying conductor. 2marks

Answers

(a) The compass needle will deflect, indicating the presence of a magnetic field around the wire.(b) If the direction of the current is reversed, the direction of the deflection of the compass needle will also reverse.(c) An electric current flowing through a conductor produces a magnetic field around it. This magnetic field exerts a force on the compass needle, which is a small magnet, causing it to deflect. The direction of the magnetic field lines is circular around the conductor, and reversing the current reverses the direction of the magnetic field.

(a) The iron filings will align themselves along circular paths, forming concentric circles around the poles of the magnet. The pattern will be denser near the poles.(b) These iron filings represent the magnetic field lines.(c) Two properties:i. Magnetic field lines emerge from the north pole and merge into the south pole.ii. The relative strength of the magnetic field is indicated by the degree of closeness of the field lines.iii. Magnetic field lines do not intersect each other.

(A) True. (R) True. The reason (R) is a correct explanation for assertion (A). If two magnetic field lines were to intersect, the compass needle at the point of intersection would point in two different directions simultaneously, which is impossible.

Given: Current

I = 5

A, distance

r = 10

= 0.1

μ_{0} = 4 π \times 10^{- 7}

T m/A.The magnetic field

B

due to a long straight conductor is given by the formula:

B = \frac{μ_{0} I}{2 π r}

Substituting the values:

B = \frac{(4 π \times 10^{- 7} T m/A) \times (5 A)}{2 π \times (0.1 m)}

B = \frac{2 \times 10^{- 7} \times 5}{0.1} T

B = \frac{10 \times 10^{- 7}}{0.1} T

B = 100 \times 10^{- 7} T

B = 1 \times 10^{- 5} T

The magnetic field at a distance of 10 cm from the wire is $1 \times 10^{- 5}$ T.

(a) If the current is doubled, the magnetic field at the centre of the coil will also double, as the magnetic field is directly proportional to the current.(b) If the number of turns is doubled, the magnetic field at the centre of the coil will also double, as the field is proportional to the number of turns.(c) The right-hand thumb rule (or Maxwell's corkscrew rule).

(a) The magnetic field lines inside the solenoid are parallel straight lines, indicating a uniform magnetic field.(b) The magnetic field inside the solenoid is uniform (constant magnitude and direction at all points).(c) A piece of a magnetic material, like soft iron, can be placed inside the solenoid. When current flows through the solenoid, the soft iron core gets magnetized, forming an electromagnet.

(a) Fleming’s left-hand rule.(b) The force experienced by the current-carrying conductor placed in a magnetic field is maximum when the direction of the current is perpendicular to the direction of the magnetic field.

(A) False. The speed and momentum of the proton may change, but its velocity might not change if the force is perpendicular to the velocity and the magnetic field is uniform (in which case it moves in a circular path). However, if the velocity is not perpendicular, the velocity will change. Assuming a general case where velocity changes. (R) True. The reason (R) is true, but it doesn't directly explain why velocity changes, only that a force exists. The force causes acceleration, thus changing velocity.

(a) Activity: Take a rectangular cardboard and make a hole in its centre. Pass a straight thick copper wire vertically through the hole. Connect the wire in series with a battery, a plug key, and a rheostat. Sprinkle iron filings on the cardboard. Close the key to pass current through the wire. Gently tap the cardboard. The iron filings will arrange themselves in the form of concentric circles around the wire. To find the direction of the magnetic field, place a compass at different points on these circles. The north pole of the compass needle will point in the direction of the magnetic field lines. Reversing the direction of current will reverse the direction of deflection of the compass needle.(b) The magnetic field strength decreases as the distance from the wire increases.

(a) Current drawn by television:

I_{T V} = \frac{P_{T V}}{V} = \frac{200 W}{220 V} \approx 0.91

A.Current drawn by fan:

I_{f a n} = \frac{P_{f a n}}{V} = \frac{100 W}{220 V} \approx 0.45

A.(b) Total current drawn

= I_{T V} + I_{f a n} \approx 0.91 A + 0.45 A \approx 1.36

A.(c) No, the fuse will not blow. The total current drawn (1.36 A) is well below the fuse rating of 5 A.

(A) True. Explanation: The electron beam moves horizontally towards the front wall. If it deflects to the right, this implies a force acting towards the right. The direction of current is opposite to the direction of motion of electrons, so current is towards the back wall. If current is towards the back wall and force is to the right, using Fleming's left-hand rule, the magnetic field must be directed upwards. (R) True. The reason (R) is a correct explanation for assertion (A).

(a) [Diagram: Concentric circles around the loop, becoming larger as they move away from the wire. Arrows indicating the direction of the magnetic field. Inside the loop, the field lines are directed perpendicular to the plane of the loop. If current is anticlockwise (viewed from above), field inside is upwards.](b) The magnetic field strength at the centre of the loop is directly proportional to the current. Therefore, if the current is increased, the magnetic field strength at the centre will also increase.

(a) The potential difference between the live wire and the neutral wire in India is 220 V.(b) The earth wire is connected to the metallic body of the appliance. If there is any leakage of current to the metallic body, the earth wire provides a low-resistance path for the current to flow into the earth. This prevents the user from getting an electric shock when they touch the appliance.

(a) Power rating

P = 2

= 2000

W, Voltage

V = 220

V.Current drawn by the heater:

I = \frac{P}{V} = \frac{2000 W}{220 V} \approx 9.09

A.(b) A 5 A fuse is rated for a maximum current of 5 A. Since the heater draws approximately 9.09 A, which is greater than 5 A, the fuse will blow. Therefore, a 5 A fuse will not protect the circuit from overloading in this case; in fact, it will prevent the appliance from working safely. A fuse with a rating higher than 9.09 A (but appropriate for safety) would be needed, or the circuit might be overloaded if other appliances are also running.

(A) True. (R) True. The reason (R) is a correct explanation for assertion (A). The interaction between the magnetic field produced by the current-carrying conductor and the external magnetic field of the horse-shoe magnet leads to a force.

(a) The direction of current in the electron beam is opposite to the direction of motion of electrons. Since the electron beam moves horizontally, let's assume it moves from left to right. Then the current is from right to left.(b) Let's assume the electron beam moves from the back wall to the front wall (e.g., towards the observer). If the electron beam is deflected downwards, using Fleming's left-hand rule:

Motion of electron (and thus current direction): Assume motion from back to front. Let's say this is along the 'x' axis.
Force: Downwards (along the negative 'y' axis).
Applying Fleming's left-hand rule: If the forefinger (field) is upwards and the thumb (force) is downwards, the middle finger (current) points from front to back.
Therefore, the magnetic field must be directed upwards.
(Note: The exact direction of initial motion needs to be specified for a definitive answer. Assuming motion into the page and deflection downwards, field would be to the left.)
Let's re-evaluate with a clearer context: If electron beam moves from back wall to front wall (e.g., East to West), and deflects downwards. Current is West to East. Force is Downwards. Using F=q(v x B), and Fleming's Left Hand Rule: Field (forefinger), Current (middle finger), Force (thumb). If current is East, force is Down. Then field must be North.
Let's assume the setup from question 6 in past paper: "electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side." If you are facing the front wall, back wall is behind you, front wall is in front. Horizontal motion from back to front. Deflection to your right. So, motion is forward, deflection is right. Current is backward. Force is right. Field (forefinger) + Current (middle finger) = Force (thumb). If current is backward and force is to the right, then magnetic field must be upwards.

(a) Fleming’s left-hand rule.(b) The magnitude of the force experienced by the conductor is directly proportional to its length. Therefore, if the length of the conductor in the magnetic field is increased, the magnitude of the force will also increase.

(a) Electromagnet.(b) Two ways to increase the strength of an electromagnet:i. Increase the current flowing through the coil.ii. Increase the number of turns in the coil.iii. Use a soft iron core (if not already present) or replace the core with a more easily magnetizable material.

(a) Separate circuits with different current ratings are used to cater to the power requirements of different appliances. Appliances with higher power ratings (like geysers, air coolers) require higher current and are connected to circuits with higher current ratings (e.g., 15 A). Appliances with lower power ratings (like bulbs, fans) require less current and are connected to circuits with lower current ratings (e.g., 5 A). This prevents overloading of individual circuits and ensures efficient power distribution.(b) During a short circuit, the insulation of wires breaks down, and the live wire and neutral wire come into direct contact. This results in a very large current flowing through the circuit. A fuse contains a wire that melts when the current exceeds a certain limit, breaking the circuit and preventing damage to appliances and the wiring.(c) Earthing is necessary for appliances with metallic bodies to provide a safety measure. If the live wire accidentally touches the metallic body, the body becomes live and can cause a severe electric shock to anyone who touches it. Earthing provides a low-resistance path for this leakage current to flow into the earth, thus keeping the potential of the metallic body at zero (earth potential) and preventing shocks.

(A) True. (R) True. The reason (R) is a correct explanation for assertion (A). The right-hand thumb rule is used to determine the direction of the magnetic field, which is observed to be in concentric circles around a straight current-carrying wire.

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Magnetic Effects of Electric Current — Competency Based Questions

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