Q: What is the correct formula for the magnetic flux $\Phi_B$ through a surface of area $A$ in a uniform magnetic field $B$, where $\theta$ is the angle between the field and the normal to the surface?

$\Phi_B = B \cdot A \cdot \cos \theta$

Q: A coil rotates in a uniform magnetic field. What is the expression for the maximum induced emf if the coil has $N$ turns, area $A$, and rotates with angular frequency $\omega$?

$\text{emf}_{\text{max}} = N B A \omega$

Question 1

Which experiment first demonstrated that an electric current produces a magnetic field around a conductor?

Accepted Answer

Oersted's experiment with a compass and wire

Question 2

What is the correct formula for the magnetic flux $\Phi_B$ through a surface of area $A$ in a uniform magnetic field $B$, where $	heta$ is the angle between the field and the normal to the surface?

Accepted Answer

$\Phi_B = B \cdot A \cdot \cos 	heta$

Question 3

According to the right-hand rule for a straight current-carrying wire, if the current flows upward, what is the direction of the magnetic field around the wire?

Accepted Answer

Counterclockwise when viewed from above

Question 4

A circular coil of radius $r$ carries a current $I$. What is the expression for the magnetic field at the center of the coil?

Accepted Answer

$B = \dfrac{\mu_0 I}{2 r}$

Question 5

Which of the following factors does NOT affect the magnitude of the magnetic force acting on a straight wire carrying current in a uniform magnetic field?

Accepted Answer

The resistance of the wire

Question 6

A solenoid of length $l$ and $N$ turns carries a current $I$. What is the formula for the magnetic field inside the solenoid?

Accepted Answer

$B = \dfrac{\mu_0 N I}{l}$

Question 7

Which law states that the induced electromotive force (emf) in a circuit is proportional to the rate of change of magnetic flux through the circuit?

Accepted Answer

Faraday's Law

Question 8

A coil is placed in a uniform magnetic field. The torque $	au$ acting on the coil is given by which formula, where $N$ is the number of turns, $I$ is the current, $A$ is the area, $B$ is the magnetic field, and $	heta$ is the angle between the normal to the coil and the field?

Accepted Answer

$	au = N I A B \sin 	heta$

Question 9

According to Lenz's Law, the direction of the induced current in a coil is such that:

Accepted Answer

It opposes the change in magnetic flux

Question 10

If the magnetic flux through a coil changes from $0.2\ 	ext{Wb}$ to $0.8\ 	ext{Wb}$ in $0.1\ 	ext{s}$, what is the magnitude of the average induced emf?

Accepted Answer

$6\ 	ext{V}$

Question 11

Which of the following best describes the shape of the magnetic field lines around a straight current-carrying conductor?

Accepted Answer

Concentric circles centered on the wire

Question 12

A transformer is used to step up the voltage from $120\ 	ext{V}$ to $480\ 	ext{V}$. If the primary coil has $100$ turns, how many turns should the secondary coil have?

Accepted Answer

$400$

Question 13

Which of the following statements about magnetic field lines is TRUE?

Accepted Answer

They form closed loops from North to South outside the magnet and South to North inside

Question 14

What is the SI unit of magnetic flux?

Accepted Answer

Weber

Question 15

A wire of length $l$ carrying current $I$ is placed perpendicular to a uniform magnetic field $B$. What is the magnitude of the force acting on the wire?

Accepted Answer

$F = B I l \sin 	heta$

Question 16

Which of the following is NOT a method to increase the magnetic field inside a solenoid?

Accepted Answer

Decrease the length of the solenoid while keeping the number of turns constant

Question 17

If the area vector of a coil is parallel to the magnetic field, what is the value of the magnetic flux through the coil?

Accepted Answer

$\Phi_B = B A$

Question 18

Which device converts mechanical energy into electrical energy using electromagnetic induction?

Accepted Answer

Electric generator

Question 19

A coil rotates in a uniform magnetic field. What is the expression for the maximum induced emf if the coil has $N$ turns, area $A$, and rotates with angular frequency $\omega$?

Accepted Answer

$	ext{emf}_{	ext{max}} = N B A \omega$

Magnetic Effects of Electric Current and Electromagnetic Induction – Physics Year 2 (STEM)

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