Resistance And Power Flashcards
Why and how are resistors rated?
Because there is a maximum that conductors can withstand before being damaged. Rated in watts and ohms.
What is a downside of using insulators?
They prevent heat loss causing possible danger of fire.
How do you know how much heat an insulator can withstand?
They will have a maximum temperature rating.
What is a plus side of heat being produced in a circuit?
It allows us to use fuses. When the temperature increases too much, fuses will blow and cut the circuit to protect the power source.
What will happen if there is a fault with some of the equipment in a circuit?
The fuse will blow.
What are fuses?
Fuses are resistors with low resistance and low melting point.
Name two types of fuses.
Cartridge fuse HRC fuse (high rupturing capacity)
What’s an advantage of using a HRC fuse instead of a cartridge fuse?
HRC fuses are safer and blow more accurately. Also, voltage present in a cartridge fuse after it has blown can cause an arc in the fuse so electricity can still pass through it. With a HRC fuse, the quartz powder inside will melt when it blows, this then flows between the two broken ends of the fuse. Quartz powder is an insulator and therefore prevents an arc occurring.
How can we safeguard against electric shock?
By earthing equipment.
What is earthing and how does it work?
When equipment is connected to the earth/sea, their electric potential is 0. The earthing cable will have no resistance, meaning current produced by a fault in equipment will flow down the earthing cable into the earth instead of flowing into the person touching the equipment causing a potentially fatal electric shock. Without this, the only path for the current to take to earth is through the person.
How are earth faults caused?
Dampness
Accidental damage
Insulation becoming hard/brittle
Why are some circuits designed for earth return?
Low voltage circuits can be designed for earth return. In a car for example, earth return means that less copper in required for wires, saving money. It also means that the car will be lighter.
What is a short circuit?
When two earths occur on one circuit, either side of a component. The current will flow through the two points of the earth, bypassing the component. This will decrease overall resistance and increase overall current, which could damage components and cause fires.
