Capacitors and/or TV (not Emf)

1. An empty capacitor does not resist the flow of current, and thus acts like a wire.

2. A capacitor that is full of charge will not allow current to flow, and thus acts like a broken wire.

RC CIRCUITS

When the switch is closed, the capacitor will begin to charge.

RC Circuits

If an isolated charged capacitor is connected across a resistor, it discharges:

RC Circuits

A battery with an emf of 24 V and an internal resistance of 1 Ω is connected to an external circuit as shown above.

1990B3p.47

a.Calculate the equivalent resistance of the combination of the 4Ω, 8Ω, and 12Ω resistors

RS = 4 + 8 = 12 Ω 1

1 1

12 12PR

= 6 Ω

1990B3 p.47

1990B3 p.47

b.Calculate the current in the 5 Ω resistor

RE = 5 + 1 + 6 = 12 Ω

E

VI

R = 2

A

24 V

12

c. Calculate the terminal voltage, VAC of the battery

VT = E - I r = 24 V - (2 A) (1 Ω)

= 22 V

1990B3

p.47

d. Calculate the rate at which energy is dissipated in the 12 Ω resistor

P = I2 R = (1 A)2 (12 Ω) = 12 W

Current splits at B with 1 A through each branch

1990B3 p.47

e. Calculate the magnitude of the potential difference VBC

VBC = I R = (2 A) (6) Ω = 12 V

1990B3 p.47

In the circuit shown above, A, B. C, and D are identical light bulbs. Assume that the battery maintains a constant potential difference between its terminals (i.e., the internal resistance of the battery is assumed to be negligible) and the resistance of each light bulb remains constant.

1998B4p.58

a. Draw a diagram of the circuit in the box , using the symbols to represent the components in your diagram. Label the resistors A, B. C, and D to refer to the corresponding light bulbs.

1998B4 p.58

b. List the bulbs in order of brightness, from brightest to least bright. If any two or more bulbs have the same brightness, state which ones. Justify your answer.A > D > B = CA has the largest currentVD = VC + VB

so D is brighter than C or BC and B are in series = same current

1998B4 p.58

c. Bulb D is then removed from its socket.

i. Describe the change in the brightness, if any, of bulb A when bulb D is removed from its socket. Justify your answer.The brightness of bulb A

decreases.REq increases, IA decreases

1998B4 p.58

ii. Describe the change in the brightness, if any, of bulb B when bulb D is removed from its socket. Justify your answer.The brightness of bulb B increases.The current through bulb B increases, voltage across B increases

1998B4 p.58

A circuit contains two resistors (10 Ω and 20 Ω) and two capacitors (12 μF and 6 μF) connected to a 6 V battery, as shown in the diagram above. The circuit has been connected for a long time.

2003B2

p.47

a. Calculate the total capacitance of the circuit.

1

1 2

1 1TC C C

1

6 6

1 1

12 10 F 6 10 F

= 4x10-6 F

2003B2 p.47

b. Calculate the current in the 10 Ω resistor.

1 2ER R R 10 20 30

E

VI

R

6 V

30 ½= 0.2 A

2003B2 p.47

c.Calculate the potential difference between points A and B.VAB = V20 = IR20

= (0.2 A)(20 Ω) = 4 V

2003B2 p.47

d.Calculate the charge stored on one plate of the 6 μF capacitor.

Q = CTV = 4x10-6 F (4 V) = 16x10-6 C

2003B2 p.47

e.The wire is cut at point P. Will the potential difference between points A and B increase, decrease, or remain the same? Justify your answer.

___increase ___decrease ___remain the same No current flows through A-B so it

does not affect the potential difference

2003B2 p.47