This document contains notes on physics concepts related to current and potential difference: - Current is defined as the flow of charge per second and is measured in Amperes. An ammeter measures current in a circuit. - Potential difference (PD) or voltage is the energy delivered per unit charge and is measured in Volts. A voltmeter measures PD across a component. - Circuit diagrams show the connections of components in series and parallel configurations and how current and PD behave differently in each.

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ICS, Abu Dhabi
Physics notes, worksheet
Name: Gr: 10 G, H
Current and potential difference
Current: The flow of charge per second.
The SI unit is the Ampere (A).
An ammeter measures the current in a circuit. It is connected in series.
Charge (Q) = current (A) x time (s)
Q = I x t I = Q / t
The conventional current direction is the direction the positive particles would travel in. This is
the opposite of what actually happens, as it is the negative particles (electrons) that move.
Conventional current goes from the positive side to the negative side.
Electron flow goes from the negative side to the positive side.
Solve the following:
1) Calculate the current flowing if a charge of 60 coulombs flows in 1 minute.

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2) Calculate the time a current of 25 milliamperes needs to flow to move a charge of 2
kilocoulombs.
3) Calculate the charge flowing when a current of 3mA flows for 1 hour.
4) a. Calculate how much charge moves past a point in 5 seconds when a current of 4A is
flowing.
b. Electrons each have a charge of - 1.6 x 10-19 coulomb. How many electrons flowed
past the point in the question above?
Potential Difference (Voltage)
•Potential difference, or PD for short, is also known as voltage.
Voltage is measured in volts (V) and is measured by a voltmeter (connected in parallel).
If a cell has 1 Volt, it delivers 1 Joule of energy to each coulomb of charge (J/C).
Voltage = Energy / Charge

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Volts = Joules / Coulomb
V = E / Q
Electro-motive force
 The emf of a cell is the work done per unit charge by the cell in moving the charge round a
complete circuit.
•The maximum voltage a cell can produce is called the electromotive force (EMF), measured in
volts.
 When a current is being supplied, the voltage is lower because of the energy wastage inside the
cell. A cell produces its maximum PD when not in a circuit and not supplying current.
Potential difference
The p.d. across a component is the work done per uni t charge in moving the charge through the
component.
(The potential difference across a component in a simple circuit is less than the emf of the cell. But for
simplicity, we assume them to be the same for calculations.)
Solve the following:
1) What is the potential energy lost by a charge of 0.2 C passing through a bulb of
potential difference 4V?
2) If 3 J of potential energy is spent by a charge of 0.4 C across a resistor, calculate the
p.d. of the resistor?

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3) Copy out and complete the table below. You may need to use the equations Q = I t
and R = V / I
voltage charge energy current time resistance
6C 18J 2s
5C 40J 5A
12V 24J 3Ω
100V 4C 8s
6A 10s 10Ω
Circuit diagram
Circuit Symbols

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Series and Parallel Circuits
Series circuit Parallel circuit
 All in a row - Different rows
 1 path for electricity - Many paths for electricity
 If 1 light goes out, the circuit is broken - If 1 light goes out, the others stay on
 e.g. switches in a circuit - e.g. household lighting
 current is the same - current is different and shared
 p.d. is different and shared - p.d.is the same
Current is the same in series, but is different and shared in parallel circuit.
Potential difference is different in series, but the same in parallel circuit.

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Solve the following:
1.
2.
3.