Ac and Capacitance Hmwk2

8/8/2019 Ac and Capacitance Hmwk2

1/5

Knox Academy Higher Physics

AC and Capacitance Homework 2

Answer all questions.

1. A student carries out three experiments to

investigate the charging of a capacitor using

a d.c. supply.

The axes of the graphs have not been

labelled.

Which row in the table shows the labels for

the axes of the graphs?

Graph 1 Graph 2 Graph 3

A Voltage

and time

Current

and time

Charge and

voltage

B Current

and time

Voltage

and time

Charge and

voltageC Current

and time

Charge and

voltage

Voltage

and time

D Charge and

voltage

Current

and time

Voltage

and time

E Voltage

and time

Charge and

voltage

Current

and time

2. Look at the circuit below.

Which of the following describes the reading

on the voltmeters a short time after switch S

is closed but before the capacitor is fully

charged?

A Vc = V1 + V2

B Vs = Vc - ( V1 + V2)

C Vs = Vc + V1 + V2

D Vs = Vc

E Vs = Vc - V1 + V2

26


2/5


3/5

3. In an experiment, the circuit shown is used to investigate the charging of a capacitor.

The power supply has an e.m.f. of 12V and negligible internal resistance. The capacitor

is initially uncharged.

Switch S is closed and the current measured during charging. The graph of charging

current against time is shown in figure 1.

(a) Sketch a graph of the voltage across the capacitor against time until the capacitor

is fully charged. Numerical values are required on both axes. 2(b) Calculate the voltage across the capacitor when the charging current is 20mA. 2

(c) How much energy is stored in the capacitor when the charging current is 20mA? 2

(d) The capacitor has a maximum working voltage of 12V.

Suggest one change to this circuit which would allow an initial charging current of

greater than 30mA. 1

(e) The 100 F capacitor is now replaced by an uncharged capacitor of unknown

capacitance and the experiment is repeated. The graph of charging current against

time for this capacitor is shown in figure 2.

By comparing figure 2 with figure 1, determine whether the capacitance of the

capacitor is greater than, equal to or less than 100 F.

You must justify your answer. 2

(9)


4/5

6. A 25 F capacitor is charged until

the potential difference across it is

500V. The charge stored in the

capacitor is

A 5.00 x 10-8C

B 2.00 x 10-5C

C 1.25 x 10-2C

D 1.25 x 104C

E 2.00 x 107C

8. The following graph shows how

the charge Q on a capacitor is

related to the p.d. V applied across

its plates.

What does the shaded area under

this graph represent?

A The distance between the

plates of the capacitor.

B The capacitance of the

capacitor.

C The working voltage of the

capacitor.

D The charge stored on the

plates of the capacitor.

E The energy stored in the

capacitor.

5. An 8 F capacitor requires

A 8 C to charge it to 1V

B 1 C to charge it to 8V

C 8 C to charge it to 8V

D 8C to charge it to 8 V

E 1C to charge it to 8 V

7. The energy stored in a 500 Fcapacitor charged to a voltage of

20V is

A 5 x 10-3J

B 2.5 x 10-2J

C 5 x 10-2J

D 1 x 10-1J

E 2 x 10-1J

4. The coulomb per volt is a unit of

A Charge

B Energy

C Power

D Capacitance

E Potential difference


5/5

9. A student investigates the charging and discharging of a 2200 F capacitor using the

circuit shown below.

The 9.0V battery has negligible internal resistance.

Initially the capacitor is uncharged and the switch is in position X.

The switch is then moved to position Y and the capacitor charges fully in 1.5s

(a) (i) Sketch a graph of the p.d. across the resistor against time while the capacitorcharges. Appropriate numerical values are required on both axes. 2

(ii) The resistor is replaced with one of higher resistance. Explain how this affects the

time taken to fully charge the capacitor. 1

(iii) At one instant during charging of the capacitor the reading on the voltmeter is

4.0V.

Calculate the charge stored by the capacitor at this instant. 3

(b) Using the same circuit in a later investigation the resistor has a resistance of 100k . Theswitch is in position Y and the capacitor is fully charged.

(i) Calculate the maximum energy stored in the capacitor. 2

(ii) The switch is moved to position X. Calculate the maximum current in the resistor. 2

(10)

Documents

Ac and Capacitance Hmwk2