Symbols

• A switch can break or complete an electric circuit. It allows a device to be used only when we need to, by switching it on or off
• Cells and batteries are power supplies for a circuit. They provide the potential difference, which drives the charges around the circuit. A battery is a collection of cells connected in series with each other.
• A lamp has a very thin filament (wire), usually made of tungsten. This gets very hot when a current flows through it, so it glows and emits visible light.
• A fuse is a safety component. It is made of a wire that has lower melting point than other components. This means that if too much current is flowing through the circuit, the wire in the fuse will melt, breaking the circuit and stopping the high current from flowing and damaging other components or devices on the circuit
• Voltmeters measure the potential difference across components in a circuit. They always need to be connected in parallel with other components. Voltmeters need to have a very big resistance so that hardly any current flows through them.
• Ammeters measure the current through a circuit. They always need to be connected in series with other components. The resistance of an ammeter needs to be as close to zero as possible so that the current reading is not affected by its presence in the circuit
• A diode lets current flow through it in one direction only. It is useful when we want to direct the current in some parts of the circuit but not in others.
• A light-emitting diode (LED) lets current flow through it in one direction only, just like a diode, but when current flows through it, it emits light.
• Fixed resistors and variable resistors resist the flow of current with a particular resistance. This means they can be used to set the current in a circuit to the value we want. Fixed resistors have a fixed value of resistance. However, variable resistors can be set to different values of resistance within a particular range.
• A thermistor is a resistor that changes its resistance when its temperature changes. Generally, the resistance of a thermistor decreases when its temperature increases
• The resistance of a light-dependent resistor (LDR) changes when the amount of light shone on it changes. Normally, LDRs have a very high resistance; when light is shone on them, their resistance drops a lot
• What is the main difference between a voltmeter and an ammeter?

  A voltmeter measures electrical voltage, while an ammeter measures electrical current.
• Explain the main difference and similarity between LEDs and diodes.

  LEDs are a specific type of diode that emits light when current passes through it, whereas diodes, in general, are semiconductor devices that allow current to flow in one direction only; the main similarity is their basic semiconductor structure.
• What components would you use in a circuit that needs to switch on when it gets dark, but only when the current flows through it in on particular direction?

  For a circuit that activates in low light and permits current flow in one direction, you could use a light-dependent resistor (LDR) for light sensing and a diode for ensuring unidirectional current flow.
• Symbols

  A) open

  B) closed

  C) cell

  D) battery

  E) diode

  F) resistor

  G) variable resistor

  H) LED

  I) lamp

  J) fuse

  K) voltmeter

  L) ammeter

  M) thermistor

  N) LDR