# Magnetic Effects Of Electric Current

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| By Tanmay Shankar
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Tanmay Shankar
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Time: 30 Minute

• 1.

### The magnetic field lines produced by a bar magnet:

• A.

Originate from the South pole and end at its North Pole

• B.

Originate from the North pole and end at its East Pole

• C.

Originate from the North Pole and end at its South Pole

• D.

Originate from the South pole and end at its West Pole

C. Originate from the North Pole and end at its South Pole
Explanation
The magnetic field lines produced by a bar magnet originate from the North Pole and end at its South Pole. This is because magnetic field lines always form closed loops, and in the case of a bar magnet, the magnetic field lines emerge from the North Pole and curve around to reenter the magnet at the South Pole. This is consistent with the convention that magnetic field lines are defined to be in the direction that a North magnetic pole would experience a force when placed in the field.

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• 2.

### A soft iron bar is inserted inside a current-carrying solenoid. The magnetic field inside the solenoid:

• A.

Will decrease

• B.

Will increase

• C.

Will become zero

• D.

Will remain the same

B. Will increase
Explanation
When a soft iron bar is inserted inside a current-carrying solenoid, it enhances the magnetic field. This is because soft iron has high magnetic permeability, which means it can easily become magnetized in the presence of an external magnetic field. As the soft iron bar is inserted into the solenoid, it aligns the magnetic domains within it, increasing the overall magnetic field strength inside the solenoid. Therefore, the correct answer is "Will increase".

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• 3.

### The north pole of Earth’s magnet is in the:

• A.

Geographical South

• B.

Geographical East

• C.

Geographical West

• D.

Geographical North

A. GeograpHical South
Explanation
The north pole of Earth's magnet is in the geographical south because magnets have two poles, north and south, and opposite poles attract each other. Therefore, the north pole of a magnet is attracted to the south pole of another magnet. Since the Earth's magnetic field is created by its internal magnetic dynamo, the north pole of the Earth's magnet is located near the geographical south pole.

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• 4.

### A current carrying conductor is held in exactly vertical direction. Inorder to produce a clockwise magnetic field around the conductor, the current should be passed in the conductor:

• A.

From top towards bottom

• B.

From left towards right

• C.

From bottom towards top

• D.

From right towards left

A. From top towards bottom
Explanation
When a current-carrying conductor is held in a vertical direction, passing the current from top towards bottom will produce a clockwise magnetic field around the conductor. This is because the direction of the magnetic field is determined by the right-hand rule, which states that if the thumb of the right hand points in the direction of the current, then the curled fingers will indicate the direction of the magnetic field. In this case, passing the current from top towards bottom will result in a clockwise magnetic field around the conductor.

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• 5.

### The force exerted on a current carrying wire placed in a magnetic field is zero when the angle between wire and the direction of magnetic field is:

D.
Explanation
The force exerted on a current carrying wire placed in a magnetic field is zero when the angle between the wire and the direction of the magnetic field is 90 degrees. This is because the force experienced by the wire is given by the equation F = I * B * L * sin(theta), where I is the current, B is the magnetic field strength, L is the length of the wire, and theta is the angle between the wire and the magnetic field. When theta is 90 degrees, sin(theta) is equal to 1, but the force becomes zero because the sine of 90 degrees is 1. Therefore, the force exerted on the wire is zero when the angle is 90 degrees.

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• 6.

### A car headlamp of 48 W works on the car battery of 12 V. The correct fuse for the circuit of this car headlamp will be:

• A.

3 A

• B.

5 A

• C.

10 A

• D.

13 A

B. 5 A
Explanation
The correct fuse for the circuit of this car headlamp will be 5 A. This can be determined by dividing the power (48 W) by the voltage (12 V) to get the current (4 A). It is important to choose a fuse with a slightly higher rating than the calculated current to ensure that it can handle the load without blowing. Therefore, the closest available option is 5 A.

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• 7.

### An induced current is produced when a magnet is moved into a coil. The magnitude of induced current does not depend on:

• A.

The speed with which the magnet is moved

• B.

The number of turns of the coil

• C.

The resistivity of the wire of the coil

• D.

The strength of the magnet

C. The resistivity of the wire of the coil
Explanation
The resistivity of the wire of the coil does not affect the magnitude of the induced current. The resistivity of a material determines how strongly it opposes the flow of electric current. However, in this case, the induced current is produced due to the changing magnetic field caused by the moving magnet, not due to the resistance of the wire. Therefore, the resistivity of the wire does not play a role in determining the magnitude of the induced current.

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• 8.

### A constant current flows in a horizontal wire in the plane of the paper from east to west as shown below, the direction of magnetic field at a point will be north to south:

• A.

Directly above the wire

• B.

Directly below the wire

• C.

At a point located in the plane of the paper, on the north side of the wire

• D.

At a point located in the plane of the paper, on the south side of the wire

B. Directly below the wire
Explanation
When a current flows through a wire, it creates a magnetic field around it. According to the right-hand rule, if you point your thumb in the direction of the current (east to west in this case), the magnetic field lines will wrap around the wire in a counter-clockwise direction. Directly below the wire, the magnetic field lines will be pointing towards the south, perpendicular to the plane of the paper. Therefore, the direction of the magnetic field at a point directly below the wire will be north to south.

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• 9.

### If two circular coils can be arrange in any of the tree situations shown in the diagram below, then their mutual induction will be:

• A.

Maximum in situation (a)

• B.

Maximum in situation (b)

• C.

Maximum in situation (c)

• D.

The same in all situations

A. Maximum in situation (a)
Explanation
The mutual induction between two circular coils is determined by the number of magnetic field lines passing through each coil. In situation (a), the two coils are positioned such that their magnetic fields are completely aligned and pass through each other, resulting in maximum mutual induction. In situations (b) and (c), the coils are either partially aligned or not aligned at all, leading to a lesser number of magnetic field lines passing through each coil and hence lower mutual induction. Therefore, the correct answer is maximum in situation (a).

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• 10.

### A coil of insulated copper wire is connected to a galvanometer forming a loop and a magnet is: A: Held stationary B: Moved away along its axis C: Moved towards along its axis There will be induced current in _________________.

• A.

A only

• B.

A and B only

• C.

B and C only

• D.

A, B and C

C. B and C only
Explanation
According to Faraday's Law of Electromagnetic Induction, an induced current is generated in a conductor when there is a change in magnetic flux through the loop. In cases B and C, the magnet is moving, which changes the magnetic flux through the coil, thus inducing a current. In case A, the magnet is stationary, so there is no change in magnetic flux, and no induced current is generated.

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• 11.

### An electric current passes through a straight wire in the direction of south to north. Magnetic compasses are placed at points A and B as shown in the figure. What is your observation?

• A.

The needle will not deflect

• B.

Only one of the needles will deflect

• C.

Both the needles will deflect in the same direction

• D.

The needles will deflect in the opposite directions

D. The needles will deflect in the opposite directions
Explanation
When an electric current passes through a straight wire, a magnetic field is created around the wire. According to the right-hand rule, the magnetic field lines will form concentric circles around the wire, with the direction of the magnetic field being counterclockwise when viewed from above the wire.

At point A, the magnetic field lines will be directed into the page, while at point B, the magnetic field lines will be directed out of the page.

Since the magnetic compass needles align themselves with the magnetic field lines, the needle at point A will deflect towards the south, while the needle at point B will deflect towards the north. Therefore, the observation is that the needles will deflect in opposite directions.

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• 12.

### A soft iron bar is introduced inside a current carrying solenoid. The magnetic field inside the solenoid:

• A.

Will become zero

• B.

Will decrease

• C.

Will increase

• D.

Will remain unaffected

C. Will increase
Explanation
When a soft iron bar is introduced inside a current carrying solenoid, the magnetic field inside the solenoid will increase. This is because the soft iron bar is a ferromagnetic material, which means it can easily magnetize and become a temporary magnet. The magnetic field produced by the solenoid induces magnetism in the soft iron bar, causing it to align its magnetic domains with the solenoid's magnetic field. This alignment strengthens the magnetic field inside the solenoid, resulting in an increase in the overall magnetic field.

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• 13.

C.
• 14.

### A 3-pin mains plug is fitted to the cable for a 1kW electric cable to be used on a 250 V ac supply. Which of the following statement is not correct?

• A.

A fuse should be fitted in a live wire

• B.

A 13 A fuse is the most appropriate value to use

• C.

The neutral wire is coloured black

• D.

The green wire should be connected to the earth pin

B. A 13 A fuse is the most appropriate value to use
Explanation
The statement "A 13 A fuse is the most appropriate value to use" is not correct. A 13 A fuse is too high for a 1kW electric cable. The appropriate fuse value should be lower than the maximum current that the cable can handle. In this case, the maximum current can be calculated using the formula P = IV, where P is the power (1kW), I is the current, and V is the voltage (250V). Rearranging the formula, we get I = P/V, which equals 4A. Therefore, a 4A fuse would be the most appropriate value to use.

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• 15.

### A current flows in a wire running between the S and N poles of a magnet lying horizontally as shown in the figure below: The force on the wire due to the magnet is directed:

• A.

From N to S

• B.

From S to N

• C.

Vertically downwards

• D.

Vertically upwards

C. Vertically downwards
Explanation
When a current flows in a wire, it creates a magnetic field around the wire. In this case, the wire is placed between the S and N poles of a magnet. According to the right-hand rule, the magnetic field created by the current in the wire will interact with the magnetic field of the magnet. The direction of the force on the wire is determined by the interaction between these two magnetic fields. Since the magnetic field of the magnet is directed from N to S, and the magnetic field created by the current in the wire is in the opposite direction, the force on the wire will be directed vertically downwards.

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• Current Version
• Jul 24, 2024
Quiz Edited by
ProProfs Editorial Team
• Feb 11, 2014
Quiz Created by
Tanmay Shankar

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