# 2.1.1 Circuit Diagrams

### Circuit Diagrams

• All students in the GCSE examination will be expected to recognise the following standard symbols and be able to construct circuits using them: • The function of the most common components are:
• Cell / battery: Provides the circuit with a source of potential difference. A battery is two or more cells
• Switch: Turn the circuit on (closed), or off (open)
• Fixed resistor: A resistor limits the flow of current. A fixed resistor has a resistance it cannot change
• Variable resistor: A resistor with a slider that can be used to change its resistance. These are often used in dimmer switches and volume controls
• Thermistor: The resistance of a thermistor depends on its temperature. As its temperature increases, its resistance decreases and vice versa
• Light-dependent resistor (LDR): The resistance of an LDR depends on the light intensity. As the light intensity increases, its resistance decreases and vice versa
• Diode: A diode allows current to flow in one direction only. They are used to convert AC to DC current
• Light-emitting diode (LED): This is equivalent to a diode and emits light when a current passes through it. These are used for aviation lighting and displays (TVs, road signs)
• Ammeter: Used to measure the current in a circuit. Connected in series with other components
• Voltmeter: Use to measure the potential difference of an electrical component. Connected in parallel with the relevant component
• Each of these components have an electrical resistance that may impact the current in the circuit
• However, the resistance of the ammeter and voltmeter are taken as negligible in exam questions

#### Drawing & Interpreting Circuit Diagrams

• Being able to draw and interpret circuit diagrams using circuit symbols is an essential skill in the electricity topic
• Electric circuit diagrams require the following to work effectively:
• An energy source – This is a source of potential difference so a current can flow. This can be a cell, battery, or a power supply
• closed path or a complete circuit – Electrons need to flow in a complete loop for a current to flow. A circuit can be open and closed using a switch
• Electrical components – These could act as sensors that respond to the environment (LDR, thermistor), or measure a value (ammeter, voltmeter), or transfer electrical energy to other forms of energy (LED, lamp). These must be drawn with the correct circuit symbol
• The key rules to remember are:
• An ammeter is always connected in series
• A voltmeter is always connected in parallel to the component the voltage is being measured
• The direction of current flow is always from the positive to the negative terminal of the power supply

#### Worked Example

Which circuit diagram correctly represents a circuit with current flowing through?  • For a circuit to be connected, the switch must be closed
• This is either circuit B or D
• The other circuit symbol is a diode
• Diodes only allow current to flow in one direction
• Since current flow is from positive to negative, a forward-biased diode must point in this direction in order for the current to flow
• This is seen in circuit B

#### Exam Tip

When asked to draw a circuit diagram, make sure to draw the wires as straight lines with a straight edge or a ruler and make it as neat as possible, especially the circuit symbols.

If the diagram is too small or there is ambiguity as to what a symbol represents, the examiner may not award you full marks! ### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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