E.m.f & Potential Difference (OCR A Level Physics)

• A cell makes one end of the circuit positive and the other negative
  • This sets up a potential difference (p.d) across the circuit

• The potential difference across a component in a circuit is defined as

The energy transferred per unit charge flowing from one point to another

• The energy transfer is from electrical energy into other forms
• Potential difference is measured in volts (V). This is the same as a Joule per coulomb (J C^-1)
  • If a bulb has a voltage of 3 V, every coulomb of charge passing through the bulb will lose 3 J of energy

• The potential difference of a power supply connected in series is always shared between all the components in the circuit

The potential difference is the voltage across each component in a circuit

• Potential difference or voltage is measured using a voltmeter
• A voltmeter is always set up in parallel to the component you are measuring the voltage for

Potential difference can be measured by connecting a voltmeter in parallel between two points in a circuit

• The difference between potential difference and e.m.f is the type of energy transfer per unit charge

• When charge passes through a resistor, for example, its electrical energy is converted to heat in the resistor
  • The resistor, therefore, has a potential difference across it

• Potential difference describes the loss of energy from charges
  • Ie. when electrical energy is transferred to other forms of energy in a component

• E.m.f. describes the transfer of energy from the power supply to electrical charges within the circuit