Topic 10 - Electricity and Circuits

What is current and how is it measured?

• Current is the flow of charged particles

• Measured in amperes (amps/A)

• Measured using an ammeter in series

• More particles flowing = higher current

• Seen in equations as I

What is potential difference and how is it measured?

• Potential difference is the energy transferred to each coulomb of charge

• Measured in volts (V)

• Measured using a voltmeter in parallel

• Stronger push = higher voltage

• Seen in equations as V

What is resistance and how is it measured?

• Resistance in how much a component opposes current

• Measured in ohms (Ω)

• More resistance = harder for charge to flow = current decreases

• Seen in equations as R

What is a series circuit and what are the rules for one?

• Components are in a continuous loop

• Current is always the same

• Voltage is shared

• Total resistance increases

What is a parallel circuit and what are the rules for one?

• Components are on separate branches

• Voltage is the same across each branch

• Current splits between branches

• Total resistance decreases

• More branches = easier for current to flow

How does a filament lamp behave and what does the graph look like?

As temperatures increase:

• Resistance increases

• Current increases more slowly

What does a diode do and what does its graph look like?

• Allows current to flow in only one direction

What does a thermistor do, what are some examples of it and what does its graph look like?

As temperature increases, resistance decreases

Examples:

• Thermometers

• Fire alarms

What is an LDR, give some examples and what does its graph look like?

• Light dependent resistor

• Higher the light intensity, lower the resistance

• Examples:

  • Street lights

  • Automatic lighting

What is power and what is it measured in?

• Power is the rate of energy transfer

• Measured in Watts (W)

What is energy measured in?

Joules (J)

What is UK’s mains?

• 230V

• 50Hz

• Alternating Current (AC)

  • Ac changes direction 50 timers per second

• Batteries produce direct current (DC)

What is the inner workings of a UK plug?

• Three wires

  • Brown = live

  • Blue = neutral

  • Green/Yellow = earth

• Fuse

• Plastic insulation

• Cable grip

What is a circuit breaker and what do they do?

• An alternative for fuses

• Detect change in current and switch off supply

• Unlike fuses, they do not break when doing this

What safety features do plugs have?

• Earth wire: stops metal cases becoming live

• Fuse: metals if current is too high

• Circuit breaker: switches off automatically

• Double insulation: plastic casing means to earth wire needed