Mains Electricity Flashcards
What is insulation and how is it used for safety?
- Insulation is covering the conducting materials in the wire (copper) with an insulating material like rubber
- It is used for safety as if a person came in contact with the conducting wire they would receive a shock, but since there is an insulator this cannot happen
What is double insulation and how is it used for safety?
- Double insulation is where insulation has already been used on the wire, but there is an additional layer of insulation around the case of the device, meaning it can never become live and can never deliver a shock upon touching it as it is not made out of metal
- These devices do not need earthing
- The symbol is a square inside a square
What is a fuse and how is it used for safety?
- Fuses are thin pieces of wire which cut off the flow of electricity if the current becomes too large
- They do this by melting at a certain value as current produces heat
What is a circuit breaker and what is its advantage over a fuse?
- A cuircuit beaker works similiarily to a fuse, except it uses an electromagnet to break the circuit when the current exceeds a certain value
- The main advantage is that you can reuse it as it does not melt
What is earthing and how is it used for safety?
- If the live wire inside of a plug came into contact with a metal casing of an appliance, the case would give anyone a shock who touched it
- However, if there is an earth wire a low resistance path back to earth would be provided, leading to a surge in current which would cause a fuse in the circuit to melt due to high currents
- This would break the cuircuit, making it safe
A surge in current occurs as current goes up when resistance goes down
In terms of energy transfers, what happens when electricity passes through a component and why?
- When current passes through a component with resistance, such as a resistor, the electrical energy is transferred to heat energy
- This is due to the electrons flowing in the conductor colliding with eachother and with ions in the lattice of ions within the metal, causing kinetic energy which is transferred into heat energy
How is the heat energy transferred to metal by current useful?
It can be used for a range of domestic appliances such as:
- Electric heaters
- Electric ovens
- Electric stove
- Toasters
- Kettles
What is the relationship between current, power and voltage?
(The symbol and word equation)
- P = I X V
- Power(Watts) = Current(Amps) x Voltage(Volts)
How do you select an appropriate fuse for its use?
- Find the current of the appliance (using equations or it may be given)
- Choose the fuse that has the next level of current up from that value
What is the relationship between energy transferred, voltage, current and time?
(The symbol and word equation)
E = I X V X T
Energy tranferred(Joules) = Current(Amps) x Voltage(Volts) x Time(Seconds)
(IV is literally just power as seen in the previous equation)
So because of this equation, you can define power as the amount of energy transferred per second
What is d.c (direct current)?
- A current in which the flow of charge is steady and constantly flowing in the same direction (positive or negative) in a circuit
- D.c power supplys have a fixed positive terminal and a fixed negative terminal
- This kind of current is produced by cells or batteries
What is a.c (alternating current)?
- A current in which the flow of charge is constantly changing direction and going back and forth between flowing in a positive or negative direction due to the voltage constantly changing between positive and negative values
- A.c power supply have two identical terminals that switch between positive or negative
- This kind of current is produced by mains electricity
- The alternation of positive and negative current can be measured with an oscilloscope as waves with a defined frequency and time period
