Practical Electricity Flashcards
Why are the heating elements of electrical appliances made of nichrome
They have high resistivity, high melting point and does not oxidise easily at high temperature
What are the formulas for power
P = IV
P = I^2 R
P = V^2/R
E = IVt
1 kWh = ? J
3.6 * 10^6 J
Why is damaged insulation a hazard
Exposed live wire can cause electric shock if touched
When insulation between live and neutral wires is damaged, may cause short circuit resulting in fire
Why is overheating of cables a hazard
Electric cable passes current that exceeds limit, large current flows through wire due to too many plugs being connected in socket, contact between plug and socket is poor, inappropriate wires used
Why is water good conductor of electricity
Water from taps usually contain charged ions and impurities that make it good conductor of electricity
Why should you wear rubber shoes when inspecting electrical fault
Rubber shoes act as insulator to cut off closed path to ground
What are circuit breakers
Electromagnetic switch that can automatically switch off electrical supply in circuit when excessive current flow through them
What is one advantage of circuit breakers
They can be manually reset without having to replace wires
What are two possible reasons for circuit breaker trips
Circuit has been overloaded
Short circuit occurred somewhere in the system
What are fuses
Safety device to prevent excessive current flow. They need to be replaced after it blows
How do fuses prevent overheating
When current exceeds rated value of the fuse, fuse will melt and open the circuit
What is function of switches
They are designed to break or complete an electrical circuit
How does earth metal casing prevent short circuit
If live wire touches metal casing of appliance, large current will flow to the earth through the earth wire and fuse in live wire will blow or circuit breaker will trip
What is color of live, neutral and earth wire
Brown, blue, green and yellow
