Physics - Domestic Electricity Flashcards
What is the unit of power used in a domestic setting?
Kilowatts (kW)
Which equation calculates how many units of electrical energy are used?
Units used (kWh) = Power (kW) x Time (h)
What are the units for E (energy transferred), P (power) and t (time) in the equation E=Pt?
E is energy transferred in joules (J), P is power in W (W) and t is time in seconds (s)
Which equation is used to calculate the cost of electrical energy?
Cost (p) = Units used (kWh) x Cost per unit (p)
What is the Fuse, and what is its purpose?
The Fuse contains a thin wire with a low melting point - if the current is too high, the wire melts, and breaks the circuit.
What is the Residual Current Circuit Breaker (rccb) and what is its purpose?
The rccb detects when there is a difference in current between the live and neutral wires. If there is a difference, the rccb trips and will switch off the circuits. It protects the user.
What is the Miniature Circuit Breaker (mcb) and what is its purpose?
The mcb detects when too much current is drawn from the mains supply. It protects the circuit, and prevents a circuit overload, or a short-circuit.
Why are circuit breakers are better than fuses?
Circuit breakers are faster acting than fuses and can be reset.
What is the function of the Ring Main?
The Ring Main delivers electricity from the consumer unit to the sockets. Arranged in parallel circuits.
What are the advantages of the Ring Main?
- Each circuit can be controlled separately
- Easy to add to the ring main because each circuit gets 230V
- The current travels in two paths so the wire can carry less current and can be made thinner
What is the Consumer Unit and what is its purpose?
The consumer unit distributes electricity from the mains supply to individual circuits within a house, and contains circuit breakers.
Which two cables does the 2 Core Cable contain?
The Live and Neutral Wire
Which three cables does the 3 Core Cable contain?
The Live, Neutral and Earth Wire
What is the function of the Live Wire?
Carries the current from the mains supply to the appliance at a high voltage
What is the function of the Neutral Wire?
Returns the current from the appliance to the mains supply at a low voltage
What is the function of the Earth Wire?
If a fault occurs and an appliance with a metal casing becomes live, the earth wire provides a safe route for the current to flow to the ground. This process is called earthing. In a normal circuit there is no current in the earth wire.
How do you calculate percentage efficiency?
% efficiency = (Energy (or power) usually transferred ÷ Total energy (or power) supplied) x 100
How do you calculate Payback Time?
Payback Time (years) = Cost of insulation (£) ÷ Money saved per year (£)
What is Alternating Current?
Alternating current (ac) is current that constantly changes in directions and magnitude (size).
What is Direct Current?
Direct current (dc) is current that has the same direction and magnitude (size).
What is the source for Alternating Current?
The Mains Supply
What is the voltage and frequency for the current that comes from the Mains Supply?
Voltage: 230V
Frequency: 50Hz
What are the sources for Direct Current?
Batteries, Cells
What is Double Insulation?
Doubly Insulated appliances are ones with protective plastic casing.
Which wire of a 3 pin plug is brown?
Live Wire
Which wire of a 3 pin plug is blue?
Neutral Wire
Which wire of a 3 pin plug is yellow and green?
Earth Wire
