Electrical Power

Question 1

What is power?

Answer 1

Power is energy used per. (Power is the rate at which energy is used up).

1 watt = 1 joule per second

Question 2

Electrical power formula’s

Answer 2

P = E/t

P = IV

P = I²R

P = V²/R

Question 3

Resistors converting electrical energy

Answer 3

Resistors convert electrical energy into heat energy.

There is a maximum power rating for resistors and other components beyond which they will overheat.

Question 4

Why is a fuse used?

Answer 4

A fuse is used to to protect the wiring from overheating in a mains electricity circuit. If a fault develops and the current becomes too high the fuse will melt to protect the flex.

Question 5

Formula for calculating fuse values for mains electricity

Answer 5

P = IV

Mains electricity = 230V

Question 6

What can electrical signals be?

Answer 6

Analogue voltages (can have any value)

Or

Digital voltages (logic 1 or logic 0)

Question 7

Resistors in a voltage divider circuit (2 resistors is series connected to a d.c. supply)

Answer 7

The largest resistor value gets the largest share of the voltage and the 2 voltages must ADD UP to the VOLTAGE SUPPLY.

Question 8

Voltage divider circuits formulas

Answer 8

V1 = (R1/R1+R2) × Vs

V2 = (R2/R1+R2) × Vs

V1/V2 = R1/R2

Question 9

What is a transistor?

Answer 9

A transistor is an electronic switch. It conducts/switches on if the input voltage is above a certain voltage.

npn transistors conduct if the input voltage is >/ 0.6V

MOSFET transistors conduct if the input voltage is >/2.4V.