How is the power of a circuit device related to its p.d and current.?
Higher p.d or higher current means more energy is transferred per second. (greater power output)
How can power be related to resistance in a circuit?
(same current) Increasing resistance increases power transfer as heat, because more energy is dissipated in the resistor
What does power rating on an appliance tell you?
The rate at which the applicants transfers energy when on at its rated p.d.
Allows comparison on how much energy different appliances use in the same time
How does the smounf of energy transferred by an appliance depend on time ?
Longer the appliance is switched on, the more total energy it transfers.
2 domestic appliances transfer energy from mains/battery to useful forms?
Kettle transfer electrical energy - thermal energy in water
Electric drills transfer electrical energy - kinetic energy of motor
Why does a high- power appliance not always use more energy than a low-power?
High power may be used for a much shorter time.
What does “Work is done when charge flows” mean?
Moving charge against resistance requires energy. This energy is transferred from power source to the circuit’s components
Why might 2 appliances with same power ratings transfer different amounts of useful energy?
Different efficiencies. Some appliances waste more energy as heat, sound , light
What is the national grid?
A system of cables and transformers linking stations to consumers.
What’s the purpose of The National Grid?
Transfers power quickly and reliably over long distances, allows electricity to be generated far from where it’s used.
What transformer is used from the power station to the transmission cables, and why?
Step up transformer - increases p.d and reduce current.
Minimises energy loss as heat in cables.
Purpose of Step-down transformers?
Decrease p.d to safe domestic levels ( 230 V). Increases current proportionally to maintain power for household use .
Why does increasing p,d improve efficiency?
For the same power, higher voltage means lower current - smaller resistive losses in cables.
Why is it dangerous to connect live wire to earth?
Creates a low resistance path for current, causing large current flow which can result in electric shock/fire.
Why can the live wire still be dangerous even if the switch is open?
Still connected to the mains supply, touching it can complete a circuit through you.
Potential difference between live wire and earth?
230 V
Function of the earth wire?
A safety wire at 0V. Carries current only if there’s a fault, prevents appliance casing from becoming live
Function of the neutral wire?
Completes circuit
Is/close to earth potential difference (0)
Function of the live wire?
Carries alternating p.d from the mains supply
What are the colour codes for mains wiring ?
Green and yellow stripes - Earth wire
Brown - Live wire
Blue - Neutral wire
What is the purpose of the 3 core cable in mains appliances ?
To carry the live, neutral and earth wires for power and safety
What is the difference between alternating p.d and direct p.d?
In alternating p.d, the direction and magnitude change repeatedly.
In Direct current, p.d stays constant in one direction
What type of current is mains in the UK?
Alternating current (ac)
Frequency; 50Hz
Potential difference; 230 V
Explain why adding resistors in parallel decrease total resistance
More paths for current to flow through
