Q: A galvanometer uses the torque on a current-carrying loop to measure current. Which physical principle allows the pointer to deflect proportionally to the current?

The torque $$\tau = NIAB \sin \phi$$ causes the loop to rotate, moving the pointer.

Q: A wire of length $$7.00 \times 10$$^{-2}$$ m is bent into a circular loop and carries a current of 4.30$ A. If placed in a 2.50$ T magnetic field, what is the maximum torque on the loop?

$$\tau_{max} = IAB$$ where $$A = \frac{l^2$}{4\pi}$$, so $$\tau_{max} = 4.30 \times \frac{(7.00 \times 10$$^{-2}$$)^2$$}{4\pi} \times 2.50$

Question 1

A rectangular loop of wire carrying current $$I is $$placed in a uniform magnetic field $$\vec{B} as $$shown in the first image. If the loop has width $$a$$ and length $$b$$, what is the expression for the maximum torque experienced by the loop?

Accepted Answer

$$	au_{max} = IabB$$

Question 2

A galvanometer uses the torque on a current-carrying loop to measure current. Which physical principle allows the pointer to deflect proportionally to the current?

Accepted Answer

The torque $$	au = NIAB \sin \phi$$ causes the loop to rotate, moving the pointer.

Question 3

In an electric motor, what is the main function of the brushes as shown in the fourth image?

Accepted Answer

To maintain electrical contact with the rotating armature and allow current to flow.

Question 4

The magnetic field at a distance $$r$$ from a long straight wire carrying current $$I is $$given by:

Accepted Answer

$$B = \frac{\mu_0$ I}{2\pi r}$$

Question 5

Two parallel wires carry currents $$I_1$$ and $$I_2 in $$the same direction, separated by distance $$d. $$What is the direction of the force between them?

Accepted Answer

The wires attract each other.

Question 6

The force per unit length between two parallel wires carrying currents $$I_1$$ and $$I_2$$ separated by distance $$d is$$:

Accepted Answer

$$\frac{F}{l} = \frac{\mu_0$ I_1$ I_2$}{2\pi d}$$

Question 7

A wire of length $$7.00 	imes 10$$^{-2}$$ m is bent into a circular loop and carries a current of 4.30$ A. If placed in a 2.50$ T magnetic field, what is the maximum torque on the loop?

Accepted Answer

$$	au_{max} = IAB$$ where $$A = \frac{l^2$}{4\pi}$$, so $$	au_{max} = 4.30 	imes \frac{(7.00 	imes 10$$^{-2}$$)^2$$}{4\pi} 	imes 2.50$

Question 8

If two parallel wires carry equal currents in opposite directions, what is the nature of the force between them?

Accepted Answer

The wires repel each other.

Question 9

A horizontal wire carries a current $$I_1 = 80$ A. A second wire 20 cm below it must carry how much current I_2$ so that it does not fall due to gravity, if the lower wire has a mass of 0.12$ g per meter?

Accepted Answer

$$I_2$$ = \frac{mg \cdot 2\pi d}{\$$mu_0$$ $$I_1$$}$$

Question 10

The magnetic field at the center of a circular loop of radius $$R$$ carrying current $$I is$$:

Accepted Answer

$$B = \frac{\mu_0$ I}{2R}$$

Question 11

Which of the following best describes the field lines around a current-carrying loop?

Accepted Answer

They resemble the field lines around a bar magnet.

Question 12

A loudspeaker uses the force on a current-carrying wire in a magnetic field. Which equation describes this force?

Accepted Answer

$$F = ILB \sin 	heta$$

Question 13

If a coil with $$N$$ turns, area $$A$$, and current $$I is $$placed in a magnetic field $$B at an $$angle $$\phi$$, what is the torque on the coil?

Accepted Answer

$$	au = N I A B \sin \phi$$

Question 14

Which scenario results in maximum torque on a current-carrying loop in a magnetic field?

Accepted Answer

When the plane of the loop is perpendicular to the magnetic field ($$\phi = 90^\circ)$$

Question 15

A current-carrying wire is placed in a uniform magnetic field. If the wire is oriented at an angle $$	heta to $$the field, what is the magnitude of the force on the wire?

Accepted Answer

$$F = ILB \sin 	heta$$

Question 16

Which of the following is NOT a real-world application of the torque on a current-carrying loop?

Accepted Answer

A transformer

Question 17

If the current in a wire is doubled, what happens to the magnetic field at a fixed distance from the wire?

Accepted Answer

The magnetic field doubles.

Question 18

Which equation would you use to calculate the net magnetic field at a point equidistant from two parallel wires carrying currents in opposite directions?

Accepted Answer

$$B_{net} = |B_1$ - B_2$|$$ where $$B_1$$ = \frac{\$$mu_0$$ $$I_1$$}{2\pi r}$$ and B_2$ = \frac{\mu_0$ I_2$}{2\pi r}$$

Magnetism: Torque, Applications, and Magnetic Fields from Currents

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