Faraday’s Law and Electromagnetic Induction Practice Problems
AP Physics
Name:
Period:
11. A loop in the form of a right triangle that has 40 cm and 50 cm long legs lies in the x-y plane. It is
surrounded by a 550 mT magnetic field in the z direction. What is the magnetic flux through the loop?
15. A square loop of wire with sides of length 40 cm faces south in a uniform magnetic field of 100 mT to the
south..
a) If the field increases to 300 mT in 0.010 s, what is the magnitude of the induced EMF around the loop?
b) What is the direction of the induced current through the wire? (as seen from the south)
c) If the field holds steady once it reaches 300 mT, what is the induced EMF in around the loop?
10. A 10 cm by 20 cm rectangular conductive loop sits horizontally inside a uniform magnetic field of 0.30 T
down. The magnetic field drops to zero in 0.45 s.
a) What is the average EMF induced around the loop as the field turns off?
b) What direction does the induced current in the loop travel? (As seen from above)
14. A magnetic field perpendicular to the plane of a wire loop with an area of 0.40 m2 decreases by 0.2 T over
10-3 s. What is the average value of the EMF induced around the loop?
16. The magnetic flux through one turn of a 60-turn coil of wire is reduced from 35 Wb to 5.0 Wb in 0.80 s,
which results in an induced current of 3.6 x 10-5 A. What is the total resistance of the wire in the coil?
17. A 2.5 W wire is curled into an elliptical loop with an area of 1.2 m2 and is placed horizontally on a table
where it is embedded in a 30 mT magnetic field that points upward. The ends of the ellipse are then pulled,
stretching it out and reducing the area to 0.1 m2. As the ellipse narrows, a current of 3.6 mA is generated in the
wire. How long does it take to change the ellipse’s shape?
18. A 10 cm radius coil of wire with 50 loops is mounted vertically so that the coils are lined up along the
north-south line. The coil is in a 1.5 T magnetic field that points east, which begins to decrease and creates an
average induced emf of 9.0 V for 20 seconds. What is value of the field at the end of the 20 s, how strong is the
magnetic field?
19. Researchers are currently working on creating wires made of plastics and other non-metallic materials.
One hope is to create elastic wires, which could stretch significantly without breaking. The experimenters in
one lab test a promising material by stretching a length of wire so it makes 10 loops around a partially inflated
balloon with a diameter of 20 cm. They place the balloon so that the loop of wire sits horizontally in a uniform
magnetic field of 0.15 T upward. Then they use a pump to add air to the balloon, increasing the diameter of the
balloon to 40 cm in 0.040 s.
a) What is the magnitude of the average EMF induced in the coil of wire? (Hint: what happens to the wire as
the balloon inflates?
b) What direction does the current flow through the coil of wire? (As seen from above.)
23. The diagram to the right shows a 20 cm long,
moveable metal rod laid on top of a rubber coated,
U-shaped wire that is 20 cm wide. The wire and rod
are in an upward pointing 0.30 T magnetic field.
The rod rolls to the left at a speed of 10 m/s.
a) What is the magnitude of the induced EMF in the
loop as the metal rod rolls?
b) What direction will the induced current flow
through the loop?
c) How large is the induced current through the rod as it rolls?
24. The flux through a fixed loop of wire changes from +40Wb to –20 Wb in –1.5 ms.
a) What does it mean for the flux to become negative?
b) What is the magnitude of the induced EMF in the loop?
25. A girls stands with an 80 cm diameter hula hoop held in one hand so that it is parallel with the ground. The
girl and hula hoop are in an upward magnetic field of 1.8 T. She lets the hula hoop slip in her hand so that it
swings downward for 0.5 s until it hangs vertically beneath her hand. What is the magnitude of the average
EMF induced in the hula hoop?