Force on a current-carrying conductor — practice questions

Question 1 · difficulty L1 · recall

The magnetic force on a straight conductor of vector length L carrying current I in field B is

• A. I(L · B)
• B. IB/L
• C. I(L × B)
• D. IL/B

Question 2 · difficulty L1 · understanding

A current-carrying wire is parallel to a uniform magnetic field. The force on the wire is

• A. ILB
• B. ILB/2
• C. IB/L
• D. zero

Question 3 · difficulty L2 · understanding

A circular coil of radius 2 cm and 125 turns carries a current of 1 A . The coil is placed in a uniform magnetic field of magnitude 0.4 T . The axis of the coil makes an angle of $30^{\circ}$ with the direction of the magnetic field. The torque acting on the coil is $\alpha \times 10^{-4} \mathrm{~N} . \mathrm{m}$. The value of $\alpha$ is $\_\_\_\_$ . $$(\pi=3.14)$$

Question 4 · difficulty L2 · understanding

A 4.0 cm long straight wire carrying a current of 8 A is placed perpendicular to a uniform magnetic field of strength 0.15 T . The magnetic force on the wire is ________mN .

Question 5 · difficulty L2 · understanding

A straight wire $$\mathrm{AB}$$ of mass $$40 \mathrm{~g}$$ and length $$50 \mathrm{~cm}$$ is suspended by a pair of flexible leads in uniform magnetic field of magnitude $$0.40 \mathrm{~T}$$ as shown in the figure. The magnitude of the current required in the wire to remove the tension in the supporting leads is ___________ A. $$\left(\right.$$ Take $$g=10 \mathrm{~ms}^{-2}$$ ).

Question 6 · difficulty L2 · understanding

Two 10 cm long, straight wires, each carrying a current of 5A are kept parallel to each other. If each wire experienced a force of 10 $$-$$5 N, then separation between the wires is ____________ cm.

Question 7 · difficulty L2 · understanding

A uniform magnetic field of $$2 \times 10^{-3} \mathrm{~T}$$ acts along positive $$Y$$-direction. A rectangular loop of sides $$20 \mathrm{~cm}$$ and $$10 \mathrm{~cm}$$ with current of $$5 \mathrm{~A}$$ is in $$Y-Z$$ plane. The current is in anticlockwise sense with reference to negative $$X$$ axis. Magnitude and direction of the torque is:

• A. $$2 \times 10^{-4} \mathrm{~N}$$- $$\mathrm{m}$$ along negative $$Z$$-direction
• B. $$2 \times 10^{-4} \mathrm{~N}$$ - $$\mathrm{m}$$ along positive $$X$$-direction
• C. $$2 \times 10^{-4} \mathrm{~N}$$ - $$\mathrm{m}$$ along positive $$Y$$-direction
• D. $$2 \times 10^{-4} \mathrm{~N}$$ - $$\mathrm{m}$$ along positive $$Z$$-direction

Question 8 · difficulty L2 · understanding

An electron is moving along the positive $$\mathrm{x}$$-axis. If the uniform magnetic field is applied parallel to the negative z-axis, then A. The electron will experience magnetic force along positive y-axis B. The electron will experience magnetic force along negative y-axis C. The electron will not experience any force in magnetic field D. The electron will continue to move along the positive $$\mathrm{x}$$-axis E. The electron will move along circular path in magnetic field Choose the correct answer from the options given below:

• A. A and E only
• B. B and D only
• C. B and E only
• D. C and D only

Question 9 · difficulty L2 · understanding

An electron is allowed to move with constant velocity along the axis of current carrying straight solenoid. A. The electron will experience magnetic force along the axis of the solenoid. B. The electron will not experience magnetic force. C. The electron will continue to move along the axis of the solenoid. D. The electron will be accelerated along the axis of the solenoid. E. The electron will follow parabolic path-inside the solenoid. Choose the correct answer from the options given below:

• A. B, C and D only
• B. B and C only
• C. A and D only
• D. B and E only

Question 10 · difficulty L2 · understanding

A current carrying rectangular loop PQRS is made of uniform wire. The length $P R=Q S=5 \mathrm{~cm}$ and $P Q=R S=100 \mathrm{~cm}$. If ammeter current reading changes from I to $2 I$, the ratio of magnetic forces per unit length on the wire $P Q$ due to wire $R S$ in the two cases respectively $\left(f_{P Q}^I: f_{P Q}^{2 t}\right)$ is:

• A. 1 : 4
• B. 1 : 3
• C. 1 : 2
• D. 1 : 5