P5. Electricity in the home Flashcards
Is mains electricty an a.c supply or d.c supply? What do each of these stand for
Mains electricity is an a.c supply
a.c. : Alternating current
d.c. : Direct current
Define alternating current and direct current
Alternating current: Current that continuously changes direction at a specific frequency
Direct current: One directional current flow
What is the frequency and voltage of the UK mains electricity supply?
Frequency: 50 Hz
Voltage: 230V
How many wires are usually in the cables connecting electrical appliances to the mains? Name these wires
- Live wire
- Neutral wire
- Earth wire
State the insulation colour used on the Earth wire.
Green and yellow stripes
State the insulation colour used on the live wire.
Brown
State the insulation colour used on the neutral wire
Blue
Explain when the Earth wire does and doesn’t carry a current.
Under normal circumstances, no current flow through the Earth wire
If a fault occurs in the appliance (such as the surge or the casing becoming live), current will flow to the ground
What potential is the neutral wire at?
0 volts
State the potential difference between the live and earth wires.
230 volts
What is the purpose of the neutral wire?
To complete the circuit by connecting the appliance back to the mains supply
For metal appliances, where is the Earth wire connected to? Why?
Earth wire is connected to the metal casing of the appliance
If live wire becomes loose and touches the casing, the current will flow through the Earth wire, preventing electrocution
State two equations for the power of a circuit. Give appropriate units
P = I V P = I² R
Power (Watts) = Current (Amperes) x Potential difference (volts)
Power (Watts) = Current² (Amperes) x Resistance (Ohms)
State an equation linking energy transferred, power and time. Give appropriate units
E = P t
Energy (Joules) = Power (Watts) × Time (Seconds)
State an equation linking energy transferred, power and time. Give appropriate units
E = Q V
Energy (Joules) = Charge (Coulombs) × Potential Difference (Volts)
What two main factors does the amount of energy transferred by an appliance depend on?
- How long the appliance is being used for
- The power of the appliance
Describe the energy transfers in a battery powered torch.
Battery converts chemical energy into electrical energy
Bulb converts electrical energy into light as well as waste energy in the form of heating
Describe the energy transfers in a battery powered motor
Battery converts chemical energy into electrical energy
Motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to friction
What three things determine the power of a circuit device?
- The potential difference across the circuit
- The current through the circuit
- The amount of energy transferred in a given time
What is the purpose of the National Grid?
To link power stations to consumers so that they have access to a source of electricity
What are two types of transformers used in the National Grid?
- Step-Up Transformers
- Step-Down Transformers
Where are step-up transformers found in the National Grid? What do they do?
Step-Up Transformers are used when connecting power stations to transmission cables
They increase the potential difference
What are step-down transformers found in the National Grid? What do they do?
Step-Down Transformers are used in connecting transmission cables to domestic buildings (like houses)
They decrease the potential difference
Why do transmission limes transfer electricity at high potentials?
A high potential, results in a low current
The lower the current, the less energy that is wasted as heat
Therefore it is more efficient
Why does the potential need to be decreased between transmission lines and houses?
Lower potentials are safer for domestic use and reduces the likelihood of severe electrocution
Appliances are designed for 230V
What can happen when insulating materials are rubbed together?
They can become (statically) electrically charged
Why can insulators become electrically charged when rubbed together?
Electrons are rubbed from one material onto the other
The material gaining electrons becomes negatively charged
The material losing electrons becomes equally positively charged
What happens when two electrically charged objects are brought close together?
They exert a force on each other
What happens when two identically charged objects are brought close together?
They exert a repulsive force on each other and repel
What happens when two oppositely charged objects are brought close together?
They exert an attractive force on each other and attract
Give an example of a non-contact force
The repulsive or attractive force acting between two electrically charged objects
What is an electric field?
A region in which a charged object will experience a non-contact electrical force
Where can electric fields be found?
Surrounding any charged object
Describe the electric field around a charged particle.
Strongest closest to the object
Decreases in strength as you move away from the object
What happens to the force between two charged objects when they are moved closer together?
The forces between them becomes stronger as the separation reduces
In situations where sparks are unwanted, what precaution must be taken to prevent the build up of static charge?
Any surfaces that are rubbing against each other should be earthed to allow the charge to flow off the materials.
