# 1.3.6 Circuits

### Constructing Circuits

• Constructing, designing and checking circuits are an essential practical skill in physics
• There are some important points to consider with all circuits:
• If the current is to be measured, an ammeter must be connected in series
• If the potential difference is to be measured, a voltmeter must be connected in parallel to the required component
• If the current is to change between two paths (eg. charging and discharging a capacitor) a switch must be present
• A diode must always be facing the direction of the current flow
• Make sure each component is able to handle the amount of current in the circuit. Otherwise, they could fuse, be damaged, or spark

Circut with corresponding circuit diagram

#### Polarity

• The polarity of an electrical component means that it will function differently depending on the direction in which it is connected
• In other words, a non-polarised components, such as a lamp can be connected in any direction it will still light up
• A polarised component can only be connected in a circuit in one direction
• If not, it will either not work, work incorrectly or break
• Common polarised electrical components include:
• Cell / batteries / any power supply
• Diodes
• LEDs (light-emitting diodes)
• Electrolytic capacitors
• The positive and negative terminal on a battery is normally clearly marked
• If not, the negative side has a larger metal area
• LEDs, and diodes consist of two pins or ‘legs’
• The longer leg is the positive (anode) pin
• The shorter leg is the negative (cathode) pin
• The polarity can sometimes be checked by multimeters and leads connected to the appropriate pins

Polarity of an LED is shown by the longer or shorter pin

#### Exam Tip

Remember to always keep the number of wires, leads and crocodile clips to a minimum. Otherwise it can become confusing as to which component is connected to which in a practical experiment

### 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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