Physics 1B Final Practice (Ch 20)
(1) Two identical loops are entering a region of uniform magnetic field as shown. They are traveling
with equal speed, but loop number 1 is traveling down and loop number 2 is traveling up.
Compare the magnitude of the induced current in the two loops. (b)
(a) I1 < I2
(b) I1 = I2
(c) I1 > I2
(2) The current in the two loops flow in the same direction (e.g. both clockwise or both counter
clockwise). (a)
(a) True
(b) False
This and the next question pertain to the following situation.
Two fixed conductors are connected by a resistor R = 20 Ω . The two fixed conductors are
separated by L = 1.5 m. A moving conductor is pushed along them (without friction) at a constant
speed v = 6 m/s. A 3 T magnetic field (shown by the black dots in the figure) points out of the
page.
(3) In which direction does the current flow through the resistor? (a)
(a) to the right
(b) to the left
(4) What force must be applied to the bar to keep it moving at 6 m/s? (b)
(a) 4 N
(b) 6 N
(c) 7.5 N
(5) A conducting wire loop is being manually rotated, at constant w = 30 rad/s. At the instant shown,
side AC is coming out of the page, and side BD is going into the page. There is a constant
magnetic field B = 0.4 T pointing to the right as shown and the loop has resistance 5 Ω.
At the instant shown, the induced current in the loop will flow: (a)
(a) clockwise.
(b) counterclockwise.
(c) No current is induced.
(6) A 4 cm × 3 cm rectangular loop is made of a wire with resistance per unit length of 25 Ohm/m.
The loop is placed in a region of uniform magnetic field, B = 5 T. The direction of B is
perpendicular to the plane of the loop and points into the page as shown.
The magnetic field starts to increase at a uniform rate of 0.1 T/sec. What is the magnitude of the
induced current in the loop?(b)
(a)
(b)
(c)
(d)
(e)
I=0A
I = 3.4 × 10-5 A
I = 1.2 × 10-4 A
I = 0.02 A
I = 4.8 A
(7) What is the direction of the induced current? (a)
(a) counterclockwise
(b) clockwise
(c) There is no induced current.
The next four problems pertain to this situation
(8) A conducting rod is sliding at a velocity v = 0.12 m/s on conducting rails, such that a rectangular
loop is formed. At time t = 0 the rod is at position l = 0.5 m (see picture). The entire device is
placed in a uniform magnetic field B = 0.45 T directed into the page. The width w = 0.4 m. The
conducting rails are long.
What is the magnetic flux Φ through the conducting loop at time t = 0 ? (b)
(a) Φ = 0 T-m2
(b) Φ = 0.09 T-m2
(c) Φ = 0.198 T-m2
(d) Φ = 0.45 T-m2
(e) Φ = 12 T-m2
(9) What is the magnetic flux Φ through the conducting loop at time t = 5 sec? (c)
(a) Φ = 0 T-m2
(b) Φ = 0.09 T-m2
(c) Φ = 0.198 T-m2
(d) Φ = 0.45 T-m2
(e) Φ = 12 T-m2
(10)
What is the induced EMF ε in the loop at time t = 5 sec? (b)
(a) ε = 0 V
(b) ε = 22 mV
(c) ε = 40 mV
(d) ε = 0.45 V
(e) ε = 12 V
(11)
What is the direction of the induced current I in the loop at time t = 5 sec? (b)
(a) clockwise
(b) counter-clockwise
(c) No current is induced.
This and the next three questions pertain to the following situation.
A circular conducting loop is placed next to a very long straight wire carrying current I (see
picture). The loop and the wire lie in a plane.
What is the direction of the induced current in the loop in each of the following cases?
(12)
The loop is held in its place: (a)
(a) No EMF is induced, hence no loop current.
(b) clockwise
(c) counter-clockwise
(13)
The loop is moved left (towards the wire) at a velocity v: (c)
(a) No EMF is induced, hence no loop current.
(b) clockwise
(c) counter-clockwise
(14)
The loop is moved up (towards the top of the page) at a velocity v: (a)
(a) No EMF is induced, hence no loop current.
(b) clockwise
(c) counter-clockwise
(15)
The current in the wire is gradually increased from I to 2I: (c)
(a) No EMF is induced, hence no loop current.
(b) clockwise
(c) counter-clockwise
This and the next two questions pertain to the following situation.
(16)
A circular conducting loop with resistance of 5 Ω and diameter d = 0.4 m surrounds a
long solenoid magnet. The solenoid consists of a coil with 2 × 104 turns/meter wrapped around a
hollow cylinder of radius R = 0.15 m. The current in the solenoid is flowing in the
counterclockwise direction producing a uniform magnetic field inside the solenoid of B = 0.75 T.
From the end view, the magnetic field at the center of the solenoid is pointing. (b)
(a) into the page.
(b) out of the page.
(17)
Calculate the magnitude of the current Is flowing in the solenoid. (c)
(a) Is = 9.5 A
(b) Is = 16.4 A
(c) Is = 29.8A
(d) Is = 58.7 A
(e) Is = 68.2 A
(18)
Now the current in the solenoid is steadily decreased to zero over a period of 5 seconds.
Calculate IL the magnitude of the average induced current in the outside loop while the current in
the solenoid is being decreased. (a)
(a) IL = 2.12 × 10-3 A
(b) IL = 2.46 × 10-3 A
(c) IL = 3.18 × 10-3 A
(d) IL = 3.76 × 10-3 A
(e) IL = 4.30 × 10-3 A