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Curcuits

Electrical circuits can be represented by circuit diagrams. The various electrical components are shown by using standard symbols in circuit diagrams. Components can be connected in series, or in parallel. The characteristics of the current and potential difference (voltage) are different in series and parallel circuits.

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Curcuit Symbols

two horizontal lines with a gap where one line is at 45 degrees  (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_a.gif)

Open Switch

two horizontal lines with a join in the centre (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_b.gif)

Closed Switch

a circle with an 'x' inside, attached to a horizontal line either side (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_c.gif)

Lamp

two 't' shapes head to head, one with a thicker top (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_d.gif)

Cell

three t-shapes, the one on left flipped to the right, the two on the right flipped 90 degrees to the left. the two on the right side have a thicker "top". (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_e.gif)

Battery

a circle with a 'V' in the centre. two horizontal lines come out from either side of the circle. (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_f.gif)

Voltmeter

 a rectangle lying flat with two horizontal lines coming out of its sides (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_g.gif)

Resistor

a rectangle lying flat with one horizontal line running through the centre of it and out of both sides (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_h.gif)

Fuse

a circle with an 'A' in the centre with two horizontal lines coming out of the sides of the circle (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_i.gif)

Ammeter

a rectangle lying flat with an arrow running through it at a 45 degree angle. two horizontal lines run out of the sides of the rectangle (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_j.gif)

Variable resistor

a rectangle lying flat with two horizontal lines running out either side of it. A 45 degree line runs through the rectangle which bends at the bottom to run parallel with the base of the rectangle (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_k.gif)

Thermistor

a rectangle lying flat with two horizontal lines running out of either side. a circle runs around the rectangle, and two arrows point downwards at the rectangle, from the top left. (http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect01_l.gif)

Light dependent resistor (LDR)

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To check for a complete circuit, follow a wire coming out of the battery with your finger. You should be able to go out of the battery, through the lamp and back to the battery.

To check for a short circuit, see if you can find a way past the lamp without going through any other component. If you can, there is a short circuit and the lamp will not light.

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Series connections

Components that are connected one after another on the same loop of the circuit are connected in series. The current that flows across each component connected in series is the same.The circuit diagram shows a circuit with two lamps connected in series. If one lamp breaks, the other lamp will not light.

(http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect02.gif)

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(http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_elect03.gif)

The circuit diagram shows a circuit with two lamps connected in parallel. If one lamp breaks, the other lamp will still light.

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Current

A current flows when an electric charge moves around a circuit. No current can flow if the circuit is broken, for example, when a switch is open. Click on the animation to see what happens to the charge when the switch is opened or closed.

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Potential difference

A typical cell produces a potential difference of 1.5V. When two or more cells are connected in series in a circuit, the total potential difference is the sum of their potential differences. For example, if two 1.5V cells are connected in series in the same direction, the total potential difference is 3.0V. If two 1.5V cells are connected in series, but in opposite directions, the total potential difference is 0V, so no current will flow.

Current

When more cells are connected in series in a circuit, they produce a bigger potential difference across its components. More current flows through the components as a result.

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Current

When two or more components are connected in series, the same current flows through each component.

Potential difference

When two or more components are connected in series, the total potential difference of the supply is shared between them. This means that if you add together the voltages across each component connected in series, the total equals the voltage of the power supply.

Check your understanding of the voltages across components connected in series using this activity.

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