212 - Problem Set 4

Physics 212 Spring 2009 Problem Set #4 Read: 17.1 – 17.4, 18.1, 18.2 and then do the problems. 1) 2)

A DVD player in a computer draws a current of 0.27 A. How many electrons pass through the player in one minute? A camcorder can run off of a charged battery pack for 2 hours. If the pack supplies 180 C of charge to the camcorder, how much current does it draw from the battery?

3)A light bulb has a filament with a resistance of 580 Ω.

A battery of 120 V is attached to the light bulb. How much current goes through the filament?

4)

A copper cable has a current of 1200 A running through it. There is a potential difference of 0.016 V between two points on the cable that are 0.24 m apart. Calculate the radius of the cable.

5)A toaster uses a nichrome heating wire.

When the toaster

is turned on at 20° C, the initial current is 1.5 A. A few seconds later, the toaster heats up and the current is 1.30 A. What is the temperature of the wire? (Hint: Set two equations equal to each other then cancel an unknown.)

6)A resistor can safely dissipate power only up to a certain rated value, beyond which the resistor becomes extremely hot and often cracks apart. What is the largest voltage that can be applied across a 680 Ω resistor, when the resistor is rated at (a) 0.25 W and (b) 2.0 W?

7)Three resistors are connected in series. Their values are 3 Ω, 5 Ω, and 8 Ω. The resistors are connected to a battery of 25 V.

a) b) c) d)

Draw a circuit diagram. Find the equivalent resistance. Find the current coming out of the battery. Using a V-I-R chart find the V and I values for each resistor.

5)362 °C

9) 14.7 Ω 10) Req = 15 Ω Ibatt = 2 A I4 = 1 A

6) a) 13 V b) 37 V

8)Three resistors are connected in parallel. Their values are 3 Ω, 5 Ω, and 8 Ω. The resistors are connected to a battery of 25

V.

9)

a) Draw a circuit diagram. b) Find the equivalent resistance. c) Find the current coming out of the battery. d) Using a V-I-R chart find the V and I values for each resistor.. Determine the equivalent resistance between points A and B for the resistors shown in the circuit below.

A 5.0 Ω

24 Ω 4.0 Ω

12 Ω

B 6.0 Ω

8.0 Ω

10)Analyze the circuit below using a V-I-R chart.

Find the Ibatt, Req, and the values of I and V for each resistor. 30 V

R2 = 18 Ω

R1 = 12 Ω

R3 = 9 Ω

R4 = 6 Ω

ANSWERS: 1) 1.0 x 1020 2) 0.025 A 3) 0.21 A 4) 9.9 mm

7) b) 16 Ω c) 1.56 A 8) b) 1.52 Ω c) 16.5 A