Most of these should look familiar to you although relays & reed switches might be new. We will discuss them on another occasion. Make sure you can draw all of these symbols from memory. You are unlikely to need to draw a reed relay but you do need to be able to recognise one, and understand how it works. If you need anything explained, please leave a comment below.
An alternative lamp symbol you may see, particularly if you are doing a practice question from an older paper, looks like this.
A reed switch (which is just a switch that can be opened and closed with a magnet) is also sometimes drawn like this.
Diodes (both light emitting and regular) only allow the current to flow in one direction. That is from the positive terminal of the battery to the negative. They block the flow of current if they are wired up the wrong way around. I would be inclined to ignore the word semiconductor in the diode’s name above – it is irrelevant at this stage of your studies!
An LDR (light dependent resistor) has a low resistance in the light and a high resistance in the dark. When light shines on it then it will allow current to pass through. In the dark it will not allow current to pass.
Questions…
- Which component converts…
- electrical energy into light energy and heat energy
- electrical energy into kinetic energy
- chemical potential energy into electrical energy
- What is the main feature that makes a diode unique?
- How does an LDR’s resistance vary with light intensity?
- An ammeter measures the current that is flowing in a circuit. Why is important that an ammeter does not add any resistance when it is connected into a circuit?
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