AQA GCSE Electricity

Equations

Theory

• Current is the flow of electrons
• Resistance obstructs the current. Less curent = More resistance. Resistance is inversely proportional to the current.
• Potential difference is energy transferred per charge passed. E.g a battery with a bigger p.d will supply more energy to the circuit for every coulomb of charge, because the charge is raised up higher at the start.
• Voltage is never obstructed by the resistance. It is constant.
• Resistance of an ohmic conductor is constant
• For a filament lamp, the higher the current, the higher the temp. meaning the higher the resistance. 
• For diodes, resistance depends on the direction of the current. Current only flows through in one direction, but have a high resistance in the other direction. 
• LDR - The brighter the light, the lower the resistance. Used in street lamps.
• Thermistor - As temp. increases, resistance decreases. Used in thermometers.
• Sensing circuits are used in LDR's and Thermistors. Fixed resistor and a fan will always have the same p.d because they are conncected in parallel. The p.d of the power supply is shared between the thermistor and the loop made up of the fixed resistor depending on their resistance. The more the resistance, the more p.d it takes.
• Series circuits: Connected in a line end to end. If one component is removed, the whole circuit doesn't work. P.d in series adds up. Total p.d is shared. The current is always the same. The resistance adds up.
• Parallel Circuits: Each component is seperately connected to the +ve and -ve. If one component is removed, it hardly affects the circuit at all. Ammeters are always connected in series. P.d is the same across all components. Current is shared betwen branches. Adding a resistor reduces the total resistance in parallel. By adding another loop, the current has more than one direction to go in. This means more current can flow. Increase in current is a decrease in resistance. 
• Mains supply is Alternating Current. Battery supply is Direct Current. Alternating current goes in multiple directions. The frequency of AC is 50Hz. Direct…