2.2 Circuit symbols and symbolism used in drawing and constructing circuit diagrams

Extended look at circuit symbols, more details, how to use them in circuit diagrams

circuit symbol for the wire in a electrical circuit.

 

circuit symbol for a T junction in the circuit wires.

 

circuit symbol for a closed switch, this completes a circuit so that it is 'on' and current can flow through the circuit.

 

circuit symbol for an open switch, this breaks a circuit so that it is 'off', and current can't flow through the circuit - you must have a continuous connected conducting material e.g. copper wire, graphite contact or an aqueous solution of ions. A switch is all about controlling the electrical activity in terms of on or off..

 

circuit symbol for a two way switch, in which one route is 'open' and the other 'closed'. These are often used in pairs so that you can switch things on and off from two different locations e.g. lights in a house on different floors.

 

, , , circuit symbols for 1, 2, 3 or many cells  wired in series

Note that >1 cell is often referred to as a 'battery'), the short stubby vertical line is the negative pole and the long thin vertical line is the positive pole in convention current notation.

Components in a series are wired in line with each other, end to end connecting with the +ve and -ve terminals of the power supply.

If you have two 1.5 V batteries wired in series, you add them up to get the total p.d. of 3.0 V.

You do exactly the same with resistors e.g. a 3.0 ohm and 5.5 resistor wired in series act as a total resistance of 8.5 ohms.

The 4th symbol often indicates a battery like that in a car, made up of multiple individual cells wired in series.

 

circuit symbol for two cells wired in parallel.

When components are wired in parallel, each one is separately connected to the +ve and -ve terminals by being connected to the main circuit at each end of the component's terminals.

If you have two cells producing the same p.d. wired in parallel, the p.d. of the circuit is just the same as one cell i.e. at either end it is the same p.d. as either cell.

 

The two symbols for an electricity supply.

 Direct current (d.c. or dc) means the current only flows in one direction and the convention current flows from positive (+) to negative (-). Electrons actually flow in the opposite direction!

  Alternating current (a.c. or ac) switches direction in a continuous oscillation e.g. 50 Hz i.e. changing direction 50 times a second.

 

circuit symbol for a resistor, which resists the flow of an electrical current e.g. in a component, often a thinner wire than the rest of the circuit wire. Resistance is measured in ohms (symbol Ω), which is usually indicated in the rectangular symbol.

 

or are circuit symbols for a variable resistor.

It behaves like any other resistor, BUT, the resistance can be varied e.g. by turning a mechanical slider like in a dimmer switch for a lamp in a room.

The more of the thin resistance wire the current goes through, the greater its resistance and the smaller the current.

In the school laboratory you may come across it as a rheostat by which you can alter the resistance by moving a slider along a resistance wire.

 

circuit symbol for a filament single lamp bulb.

circuit symbols for two lamp bulbs wired in series etc.

 

circuit symbols for two lamp bulbs wired in parallel.

 

circuit symbol for a voltmeter that measures the potential difference in volts (p.d. in V).

The voltmeter is always wired in parallel across another circuit component to measure the p.d. in volts across it. The term voltage is usually acceptable, but the more correct term is potential difference (p.d. in volts).

 

circuit symbol for an ammeter, an instrument that measures the flow of electrical current in amps (A). Current flow is the movement of electrical charge carried by electrons.

The ammeter is always wired in series at aa particular point in a circuit, but this may be in a section of a parallel circuit system, depending on which part of a circuit you want to know the current flow.

You may come across a galvanometer, a very sensitive electromechanical instrument used to detect and measure tiny electric currents. When a tiny electrical current passes through its internal coil, it produces a magnetic field that interacts with a permanent magnet, causing a sensitive needle to deflect and display an electrical current and its direction

 

circuit symbol for a fuse. This melts and breaks the circuit if the current increases above a safe limit. Excess electrical energy is converted into excess thermal energy, sufficient to melt the fuse wire.

 

circuit symbol for a semi-conductor diode, sometimes the symbol is enclosed in a circle (semi-conducting diode)

A diode only allows a current to flow in one direction and so is used in control circuits.

 

circuit symbol for a thermistor whose resistance changes with temperature i.e. the current allowed to flow varies with temperature and is used in control circuits

 

circuit symbol for a light emitting diode (an LED), a semiconductor device that changes electrical energy into light energy i.e. it glows when a potential difference (voltage) is applied across it.

In terms of electrical energy to light transfer, it is a much more efficient device than a hot filament lamp bulb and is a very useful device indicator lights and torches.

 

circuit symbol for a light dependant resistor (LDR), sometimes the rectangle is enclosed in a circle

The resistance of an LDR changes depending on the intensity of light that shines on it.

The greater the light intensity, the lower the resistance and the greater the current flow, hence its use in lighting control circuits.

 

circuit symbol for an electric motor, sometimes its just a circle with an M in it

Circuit symbols (as far as I know) NOT needed for UK GCSE physics courses ???

circuit symbol for capacitor, a device that stores energy in the form of electrically charged field between its plates.

circuit symbol for microphone, that converts a sound wave into an electrical signal.

circuit symbol for loudspeaker, that converts an electrical energy signal into sound energy.

circuit symbol for a transformer, which converts an a.c. current of one voltage in one input coil into an a.c. current of a different voltage in a second output coil.

circuit symbol for a bell.

circuit symbol for a buzzer.

Lots of electrical (electronic) circuit symbols - how many can you identify?