Practing Equations

Question 1

(a) A rechargeable battery is put on charge for 4.0 hours with a constant current of
50 mA from a 6.0 V supply. Calculate
(i) the charge which flows through the battery in this time
charge = …………………………………………….. C

Answer 1

(a) Q = It = 0.050 x 4.0 x 3600 = 720 C (1)

Question 2

(ii) the energy which has been provided from the supply.
energy = ……………………………………………… J
[2]

Answer 2

E = QV with knowledge of what the symbols mean (1)

= 720 x 6.0 = 4320 J (1)

Question 3

(b) In what form does a battery store energy?
………………………………………. energy
[1]

Answer 3

chemical (potential energy)

Question 4

The charged battery has an e.m.f of 4.5 V and is connected to a 48 Ω resistor.
The potential difference across the resistor is found to be 4.0 V. The current is
constant during the 45 minutes the battery discharges. Calculate
(i) the internal resistance of the battery when in use
internal resistance = …………………………………………….. Ω
[2]

Answer 4

I = 4.0/48 = 0.0833 (A) (1)
Vr = 0.5 V (1)
r = 0.5/0.0833 = 6 Ω (1)

Question 5

The charged battery has an e.m.f of 4.5 V and is connected to a 48 Ω resistor.
The potential difference across the resistor is found to be 4.0 V. The current is
constant during the 45 minutes the battery discharges. Calculate

the energy supplied to the 48 Ω resistor in this time

Answer 5

E = V2
t/R with knowledge of what the symbols mean (1)
= 4.02
x 2700 / 48 = 900J (1)

Question 6

A circuit with a cell of 3V, with 2 voltmeters in series. What is the voltage in one of the voltmeters?

Answer 6

1.5V

Question 7

A circuit with a cell of 3V, with 2 voltmeters in parallel. What is the voltage in one of the voltmeters?

Answer 7

3V

Question 8

A circuit with 6A, with 2 ammeter in series. What is the current in one of the ammeters?

Answer 8

6A

Question 9

A circuit with 6A, with 2 ammeter parallel. What is the current in one of the ammeters?

Answer 9

3A

Question 10

12 V power pack; potential divider dividing into 6ohms and 4ohms. What would be the voltage in each

Answer 10

7.2 and 4.8 respectively

Question 11

a) A cell provides 76C of charge with 120J of energy. What is the cell’s emf?
b) When a lamp carries a current of 2.4A for 5.4s, it transfers 120J of energy. What is the pd across the lamp

Answer 11

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