Electrical working, ion lattice, heating and electrical safety Flashcards
Electric Current and Resistor Heating
When there is an electric current in a resistor, energy is transferred to heat the resistor.
Energy Dissipation and Resistance
Electrical energy is dissipated as thermal energy in the surroundings when an electric current does work against electrical resistance.
Energy Transfer in Resistors
The energy transfer in resistors is due to collisions between electrons and ions in the lattice, which causes the material to heat up.
Reducing Unwanted Energy Transfer
Unwanted energy transfer can be reduced by using low-resistance wires, which minimize energy loss as heat.
Heating Effect of Electric Current
Advantages:
Useful in heating devices like kettles,
toasters.
Disadvantages:
Can cause energy waste in unwanted areas, like wires in electronic devices.
Equation for Energy Transfer
Equation:
Energy transferred (J) = Current (A) × Potential Difference (V) × Time (s)
Formula:
E = I × V × t
Power and Energy
Power is the energy transferred per second and is measured in watts (W).
Power Equation
Equation:
Power (W) = Energy transferred (J) ÷ Time taken (s)
Formula:
P = E ÷ t
Power Transfer in Circuit Devices
Power transfer in any circuit device is related to the potential difference across it and the current passing through it.
Electrical Power Equations
Equations:
Electrical power (W) = Current (A) × Potential Difference (V)
Formula: P = I × V
Electrical power (W) = Current² (A²) × Resistance (Ω)
Formula: P = I² × R
Energy Transfer in Domestic Devices
In domestic devices, energy from batteries and a.c. mains is transferred to motors or heating elements (e.g., in microwaves or heaters).
Direct vs Alternating Voltage
Direct voltage stays constant in one direction, while alternating voltage regularly reverses direction.
Direct Current (D.C.)
Direct current (D.C.) is the movement of charge in one direction only. Cells and batteries supply D.C.
Alternating Current (A.C.)
Alternating current (A.C.) is where the movement of charge changes direction periodically.
UK Domestic A.C. Supply
UK Domestic A.C. Supply
Live and Neutral Wires
Live wire: Carries the current to the appliance.
Neutral wire: Completes the circuit by carrying the current back.
Earth Wire and Fuses
The earth wire provides a path for current to the ground in case of a fault. Fuses or circuit breakers protect circuits by disconnecting when current exceeds safe limits.
Position of Switches and Fuses
Switches and fuses should be connected in the live wire to cut off the supply to the appliance completely.
Mains Wire Potential Differences
Live wire: ~230 V
Neutral wire: ~0 V
Earth wire: 0 V (for safety)
Dangers of Live to Earth Connection
Connecting the live wire to earth can cause a dangerous short circuit, leading to electric shocks or fire.
Power Ratings and Energy Changes
The power ratings of domestic appliances reflect how much energy they transfer per second, such as heaters converting electrical energy into thermal energy.
