## DC Circuits

## Symbols

## Electromotive Force (e.m.f)

**Energy transferred through a power supply per unit coulomb in a circuit. It is the conversion of chemical energy into electrical energy**

## Potential Difference

**Energy transferred through a circuit per unit coulomb. It is the conversion of electrical into other energy**

**E.m.f or p.d. (V) V =**

__W__Energy transferred/Work done (J)**Q Charge (C)**

## Kirchhoff's Second Law

**The total voltage across a circuit loop is equal to the sum of the voltage drops across the components in that loop.**

## Types of Circuit

## Series

**How to work out the overall resistance**

Use Kirchhoff's second law

So:

**VTot = V1 + V2 + V3 etc.**

**VTot = IRTot**

**IRTot = I(R1 + R2 + R3 etc.)**

'I' cancels out giving

**RTot = R1 + R2 + R3 etc.**

## Parallel

**How to work out the overall resistance**

Use Kirchhoff's first law

So:

**ITot = I1 + I2 + I3 etc.**

**ITot = V/RTot**

**V/RTot = V(1/R1 + 1/R2 + 1/R3 etc.)**

'V' cancels out

**1/RTot =**

**1/R1 + 1/R2 + 1/R3 etc.**

The total resistance is lower than all of the other resistance values

## Potential Divider

Used to

**divide**the**voltage between resistors**. This is done through a circuit with**resistors in series**.To work out the Voltage over a resistor you can use the equation.

**V1 =**

R1 + R2__R1__x VinR1 + R2

## Power

**The rate of**energy transfer

**in a**unit time

**. Measured in**Watts

**Power (W or J/s) P =**

__W__Work Done (J)**t Time (s)**

Large appliances are usually measured in

**kilowatts**

Companies keep track of how much electricity is being supplied in**kilowatt hours (kWh)**

Kilowatthour - the amount of energy used by a 1 kW appliance every hour

This is worked out by

Power in kWKilowatthour - the amount of energy used by a 1 kW appliance every hour

This is worked out by

Power in kW

__multiplied__by time in hours = kWh