When two resistors are connected in series across a 12-V battery, 1.1A flows. Wh

Question

When two resistors are connected in series across a 12-V battery, 1.1A flows. When they are connected in parallel across the same battery, 6.3 A flows. What is the smaller resistors value?
a. 8.4
b. 1.7
c. 0.55
d. 2.5 ohms


2. A 7.5m long extension cord carries a current of 12 amps. The cord is made of two wires, carrying currents in opposite directions, separated by a distance of 4.9mm. Find the force between those two wires.
a. 0.0059N
b. 1.2 N
c. 0.33 N
d. 9.0N
e. 0.044 N

3. A car antenna is 1.5 m long. The car is moving at 15 m/s in a region where the earth's magnetic fieldis 4.5 x 10^-5 T and is directed perpendicualr to the length of the antenna. What emf is induced in the antenna?
a. 1.0 mV
b. 3.0mV
c.4.5 mV
d. 2.0mV

4. After the switch is closed in a series LR circuit, what is the current when a time equal to four time constants has elapsed?
a. 0.98Imax
b. (1/16)Imax
c.0.018I max
d.(1/5)Imax
e.(15/16)Imax

5. A circular coil lays flat on a horizontal table in a region where the magnetic field is straight down. The magnetic field is suddenly removed. When viewed from above, what is the direction of the current in the coil as the field is removed?
a. there is no induced current
b.clockwise initially, then counter-counterclockwise before going to zero
c. counter-clockwise
d.clockwise

Explanation / Answer

4. After the switch is closed in a series LR circuit, what is the current when a time equal to four time constants has elapsed?
a. 0.98Imax
b. (1/16)Imax
c.0.018I max
d.(1/5)Imax
e.(15/16)Imax

ANSWER:
i = Imax e^(-4?/?) = i(0) e^(-4) = 0.018 Imax
answer is "c.0.018 Imax"

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