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# Physics Year 10 tracked homework 5: Current and potential difference

## Data: The magnitude of the charge of an electron is 1.602 × 10−19 C

ALL

1 Draw the circuit symbol for the following circuit components: [4 marks]
a. cell
b. battery
c. fuse
d. resistor

2 State the name of the meter which is used to measure current [1 mark]

3 A pupil is told that the meter used to measure the current through a bulb is Teacher
connected in series with the bulb but that a meter used to measure the potential marked
difference across a bulb is connected in parallel with the bulb.

With the aid of suitable diagrams explain what is meant by in series and in parallel
when the terms are used as above.

4 State the amount of charge that will have flowed through a resistor in 1 minute if [3 marks]
a current through the resistor is 0.25 A

MOST

5 A scientist working with very small currents measures charge of 0.2 mC flowing [4 marks]
through a diode over an hour.

Calculate the current through the diode giving your answer in standard form to
two significant figures

6 In everyday language we talk about batteries being charged and discharged. Teacher
However the total amount of charge in the battery is always zero (for every marked
electron in the battery there is a proton hence the total amount of negative
charge is equal to the total amount of positive charge the net charge is zero). Also
every time an electron leaves the negative terminal of the battery an electron
enters the positive terminal so during operation the battery neither gains nor
loses charge.

During normal operation the battery exhaust its chemical energy store and
enables electrical work to be done in the circuit into which the battery has been
connected. In January 2018 you could buy a “USB power bank” (i.e. a battery)
rated at “13,200 mA h” for £50. “13,200 mA h” means that the amount of charge
that will flow whilst the power bank fully transfers its store of energy to other
stores is the same as the amount of charge that would move when a current of
13,200 mA flowed for 1 hour.

The USB cable connecting a mobile phone to the “power bank” makes separate
connections to the positive and negative terminals of the battery. Calculate the
charge that flows across one of the terminals of a “13,200 mA h power bank”
when you fully discharge the power bank.

7 LED torches are highly efficient. Let us assume that they are 100% efficient and
that therefore all the chemical energy transferred from the chemical stores of the
battery is transferred usefully firstly via the electrical work pathway and then via
Physics Year 10 tracked homework 5: Current and potential difference

The LED torch is used for 2 minutes. Whilst it is being used current of 0.06 A flows
across a potential difference of 2.3 V.

a) Calculate the charge that flows whilst the torch is being used [2 marks]
b) Calculate the energy usefully transferred as visible light during the time [2 marks]
the torch is on

SOME

8 A physicist builds an electron beam. The electrons travel in single file. They move
at 10% of the speed of light and there is a distance of 1.2 metres between each
electron and the electron in front of it.

## a) What is the current of the electron beam? [2 marks]

b) What happens to the current if electrons are replaced with He2+ ions? [2 marks]

## 9 The diagram below shows a very simple cell Teacher

marked

As zinc is more reactive than copper if zinc was placed directly into the copper
sulphate solution a displacement reaction would occur producing zinc sulphate
and copper. The same reaction can occur indirectly as shown above and the
chemical energy transferred as the chemical energy store of the reactants is
reduced can be transferred to other stores via electrical work as electrons move
between the electrodes.

Zinc atoms in the zinc electron and ‘give away’ two electrons forming Zn2+ ions
which are added to the zinc sulphate solution surrounding the zinc electrode. At
the same time Cu2+ ions from the copper sulphate solution surrounding the copper
electrode ‘collect’ electrons from the copper electrode and form neutral copper
atoms.

If the cell provides potential difference of 1.10 V, how much energy is transferred
from the chemical energy store each time two electrons ‘given away’ by a zinc
atom in the zinc electrode are ‘collected’ by a copper ion at the copper electrode?
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