A few important terms you will have to know in I/GCSE Physics:
- Current = flow of electric charge round the circuit. Unit = ampere, A
- Potential Difference (voltage - they're the same thing) = Driving force that pushes the current round. Unit: volt, V
- Work Done = the energy transferred. Unit = joules, J
- Resistance = anything within the circuit that slows the flow down. Unit: ohm,Ω
The greater the resistance across a component, the smaller the current that flows
Total charge through a circuit depends on current and time:
- Current is the rate of flow of charge.
- Current = charge / time
- Current (I) = charge (Q) / time (t)
- I = Q/t
- Current (I) is measured in amps (A)
- Charge (Q) is measured in coulombs (C)
- Time (t) is measured in seconds (s)
- More charge passes around the circuit when a bigger current flows
Potentical Difference (Voltage)
Potential difference (or voltage) is the work done (the energy transferred, measured in joules, J) per coulomb of charge that passes between two points in a circuit. The formula for this is - P.D. = Work Done/Charge. So the potential difference is the amount of energy transferred by the electrical component (eg light and heat energy by a bulb) per unit of charge.
A voltmeter measures the potential difference between two points.
- A battery transfers energy to the charge as it passes (the push that moves the charge along)
- Components transfer energy away from the charge (to use a lamp eg)
- Voltage of a battery shows how much work the battery will do to the charge that passes through it (how big of a push it gives)
- Voltmeter is used to measure the potential difference between two points
- The voltmeter is placed in parallel with a component so it can compare the energy the charge has before and after passing through the component
- Measures the current (in amps) flowing through the component
- Must be placed in series
- Can be put anywhere in series in the main circuit, but never in parallel like the voltmeter
- When an electrical charge flows through a resistor, some of the electrical energy is transferred to heat energy; this means the resistor gets hot
- This heat causes ions in the conductor to vibrate more
- This makes it more difficult for the charge-carrying electrons to get through the resistor (the current can't flow as easily and the resistance increases)
- Most resistors have a limit to the amount of current that can flow
- More current means an increase in temperature which means an increase in resistance, which means the current decreases again
Potential Difference = Current x Resistance V = I x R
V-I Graphis show how the current varies as you change the potential difference.
Different Resistors - The current through a resistor is directly proportional to P.D. Different resistors have different resistances, so this means different slopes.
Filament Lamp - As the temperature of the filament increases, the resistance increases, hence the curve.
Diode - Current will only flow through a diode in one direction. The diode has very high resistance in the opposite direction.
Current only flows in one direction through a diode. They are used to regulate the potential difference in circuits. It lets current flow freely in one direction, but not in the other - high resistance on this side.
Light Emitting Diodes (LED) - 💡
emits light when a current flows through it in a forward direction. They use a much smaller current than other forms of lighting. They indicate the presence of current in a circuit. They're used in TVs for example to show they are switched on. They're also used for numbers on digital clocks, traffic lights and remotes.
Light - Dependent Resistor (LDR) - 💡
dependent on the intensity of light. In bright light, the resistance falls. In darkness, the resistance is high. They have lots of uses including automatic night lights, outdoor lights and burglar detectors.
temperature dependent resistor. In hot conditions, the resistance drops. In cool conditions, the resistance goes up. They make useful temperature detectors, e.g. car engine temperature sensors and electronic thermostats.
Drafted by Catrina (Physics)