7. Suppose you have a 100 turn solenoid and pull it out quickly. The solenoid is

Question

7. Suppose you have a 100 turn solenoid and pull it out quickly. The solenoid is 12 cm on a side and has a resistance of 75 ohms and is being pulled out ofa5T magnetic field in 0.25 seconds. What is the induced current running thru the A. 0.7 A B. 1A C. 0.14A D. 40 A E 0.4 A solenoid? 8. How costs $0.08/kWh? much does it cost to operate a 25 W soldering iron for 8 hours, if energy A. $1.50 B.S0.25 C.$0.16 D. $2.50 E.S0.016 9. Two parallel wires earry identical currents in opposite directions. What is the direction on the net magnetic field at point P? 2 A. Left B. Right C. Top of page D. Bottom of page E. Into the page 10. A 12 volt battery has a terminal voltage of 10 volts when delivering a current of 20 A to the starter of a car. What is the internal resistance of the battery? A. 0.1 ohm B. 2 ohm C.1.2 ohm E. 0.5 ohm 11. Two parallel wires carry currents I, and L in the same direction and separated by a distance d. The magnitude of the magnetic force between the wires is F o. What is the force per length between the wires if each current is doubled and the separation is halved? Fo D.8 Fo E.16F

Explanation / Answer

7.

i = EMF/R

R = 75 ohm

EMF = -N*d(phi)/dt

phi = magnetic flux = B*A

EMF = -N*A*dB/dt

EMF = -100*12*12*10^-4*(0 - 5)/0.25 = 28.8 V

Now

i = 28.8/75 = 0.38 Amp = 0.4 Amp

Correct option is E.

8.

Power = 25 W

time = 8 hr

Energy required = P*t

E = 25*8 = 200 W-hr = 0.2 kWh

Price of 1 kWh = 0.08 cents

Price of 0.2 kWh = 0.08*0.2 = 0.016 cents

Correct option is E.

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