# Let’s Get Physics-l: Circuit Symbols

Slightly overdue considering my promise of a 1-post-per-week minimum for this feature but we are here now so lets get cracking. Having now started Physics Physics (As opposed to Maths Physics) with electricity, lets cover a vital topic which will be needed for posts to come (I refuse to let this feature die): Circuit Symbols
There are many circuit symbols that depict the numerous components that can make up a circuit. The ones listed below are the ones deemed a necessity for A-level which you should try and learn (If you are doing A-level, otherwise don’t feel pressured to):
 Symbol Name Description Resistance Switch Turns an electric current on and off by connecting and disconnecting wires When closed the resistance is very low but when open the resistance is very high because current can’t jump (Don’t say jump the gap in your exam (But by all means do when discussing Physics with your friends)! The current simply has nothing to pass through) the gap. Cell Provides the circuit with a source of energy (J) or electromotive force (V) Cell’s have a negligible resistance or a low internal resistance (It would very bad if the source of energy for a circuit doesn’t let current flow easily). Battery As with the cell, a battery provides a source of energy (Chemical to Electrical for anyone who is interested) or e.m.f. Batteries have two or more cells. Equal to cells but the resistance will increase with the addition of more cells (e.g. If Iron man activated the House Party Protocol (Click here for more) It becomes harder for the bad guys to beat him). Terminals (In this instance a DC Power Supply) As with cells and batteries, these provide energy or e.m.f. These include DC Power Supplies and AC Power Supplies. Low, as with the battery and cell. Bulb (Lamp when illuminated) When current passes through the bulb it transfers electrical energy to light energy. The Resistance increases as the current increases. As the bulb heats up (Heat energy is produced as waste) the atoms within begin to vibrate more which cause more collisions with atoms and free electrons, reducing the flow of current. Fixed Resistor Controls the amount of electric current flowing in a circuit or through a component. It has a fixed resistance and this depends on the material it is made from. They are often made from Semi-conductors such as Silicon. Variable Resistor Controls the amount of electric current flowing through a component. The resistance is dependent on the position of the slider or dial (which allow the current to flow through at different rates). Fuse This is a safety device. It melts when the current gets to high – also known as “blowing”. Typically low and really depends on the thickness and material of the wire. It has to let current flow through or it defeats the point of melting when it gets too high. Heater This transfers electrical energy to heat energy (Which I imagine you guessed but hey-ho). Typically high due to the high temperatures vibrating the atoms within. Ammeter It measures the flow of current around a circuit or a component (If so then it is in parallel to the component). Very Low Voltmeter It measures the electromotive force or potential difference across a component. Very High – It has to be in parallel to the component else it will block the current. Thermistor Responds to the temperature if the environment and changes its resistance consequently. Dependent on the temperature of the environment – High Temperatures produces low resistance and vice versa Diode It enables current to flow through one way. They are used as a shield, of sorts, for more delicate components against high currents. The resistance is very low in the forward direction but very high in the reverse direction. Light-Emitting Diode As with the diode, current can only flow through it one way. When current passes through it the LED emits light. The resistance is very low in the forward direction but very high in the reverse direction. Light-Dependent Resistor This changes the flow of current when the light intensity changes. The resistance decreases as light intensity increases (Sort of like a night-day cycle in the way that less current/electrical energy gets through when darker, similar to how we feel tired (Unless you are in fact nocturnal) and more current goes through when lighter like when we feel more awake during the day (Or not (It is rather subjective))).

These components can be combined together to make a multitude of different circuits all with different purposes. For example, a switch, cell, bulb and some wires create a basic torch. A battery, heater and some wires can be combined to make a simple heating system. The list goes on and  it depends, really, on your need and the capabilities of each component.

This is really all that needs to be known about circuit symbols for the time being. If there are any ones that you aren’t sure about or you would like to see me struggle to devise an example please ask in the comments and I would be happy to oblige (As best I can).

Just to give you a heads up, I will hopefully be publishing some posts about types of circuits, the two different types of current flow and Charge, Current and Drift Velocity (These might warrant solo posts but I have yet to decide). If these topics don’t sound particularly exciting then please make any suggestions (It will provide me with far more encouragement to post if people do make requests but don’t feel you have to). If you have any thoughts, questions or feedback please leave them in the comments.