0

1. FUNDAMENTAL Physics – Circuits: 3.2 Current and Charge
Electrical Analogy, Current and Charge
Learning Outcomes
• I can describe a useful analogy for an electrical circuit
• I know the definitions, units and symbols for charge, current and time
• I know the relationship between Charge, Current and time
• I know symbols used when drawing electrical circuit diagrams
• I can describe current, voltage and resistance
An electrical Circuit is like a hot water system.
Analogy
Electrical
Component
Is like the….. Because…. (any short
comings in the
analogy)
Battery Boiler It supplies
energy to the
circuit.
Charge
(electrons)
Water It flows
around the
circuit and
carries energy
Wire Water pipes It carries the
charge/water
Water will leak
from a pipe, but
electrons will
not ‘leak’ from
a broken wire
1

2. FUNDAMENTAL Physics – Circuits: 3.2 Current and Charge
Lamp Radiator/heater The
lamp/heater
transfers
energy from
the circuit to
the
surrounding
A* mark”
Potential
difference in
the circuit
(across the
lamp)
Temperature
difference in
the water
(before and
after the
heater)
This is a
measure of the
energy
transferred.
2

3. FUNDAMENTAL Physics – Circuits: 3.2 Current and Charge
Charge
What is the relationship between charge and current?
Definition: Current is the rate of flow of charge.
Current = Charge / time
Current I is measured in Amps A.
Charge Q is measured in Coulombs C.
Time t is measured in seconds s.
Practice Question
Q1. A bucket can hold 12kg of water. A tap
starts to fill the bucket at a flow rate of 0.10kg/s.
Calculate the time taken to fill the bucket.
Q=It
12/0.1=120s
Q2. A battery delivers a current of 1.2A to a circuit. After 2.0mins
how much charge has moved around the circuit?
I=1.2A
t=120
Q=It
=1.2x120
=144 coulombs
3

4. FUNDAMENTAL Physics – Circuits: 3.2 Current and Charge
Electrical Symbols
Identify these common symbols used in circuits.
……Lead…… ……Resistor….
……Cell…… ……Battery….
…Power Pack… …Variable Resistor…
…Ammeter… ……Voltmeter….
……Lamp…… ……Switch….
..Push Button Switch.. …Two way switch.
…Fuse… …… Pokemon….
4
A V

5. FUNDAMENTAL Physics – Circuits: 3.2 Current and Charge
Electrical Basics
We need to define some basic properties in electricity:
Charge
The unit of Charge is the Coulomb .
The symbol for charge is Q .
The symbol for the Coulomb is C .
Current
Current is the rate of flow of charge.
Current is measured using an ammeter .
The unit of Current is the Ampere , or Amp .
The symbol for Current is I .
The symbol for the Amp is A .
Potential Difference
(Potential Difference is the push that makes charge move.)
Potential Difference is the energy supplied to the charges
Potential Difference is measured using a voltmeter .
The unit of Potential Difference is the Volt .
The symbol for Potential Difference is V .
The symbol for the Volt is V .
5
A
V

6. FUNDAMENTAL Physics – Circuits: 3.2 Current and Charge
Resistance
Resistance resists the flow of charge and reduces the current.
Resistance is calculated from Potential Difference and Current.
The unit of Resistance is the Ohm .
The symbol for Resistance is R .
The symbol for the Ohm is Ω.
Home work:
• P177, Q 3-4
• P 179, Q 1-2
• Worksheet ‘Current and Charge’
6

7. FUNDAMENTAL Physics – Circuits: 3.2 Current and Charge
Resistance
Resistance resists the flow of charge and reduces the current.
Resistance is calculated from Potential Difference and Current.
The unit of Resistance is the Ohm .
The symbol for Resistance is R .
The symbol for the Ohm is Ω.
Home work:
• P177, Q 3-4
• P 179, Q 1-2
• Worksheet ‘Current and Charge’
6