Power and electricity

Question 1

What is meant by the term power?

Answer 1

The rate of energy transfer

-Power = Current x Voltage

Question 2

Formula for input power and output power

Answer 2

Voltage P x current P = Voltage S x Current S

Question 3

How does a step-down transformer work?

Answer 3

-The turns on the primary coil are greater than the turns on the secondary coil
-The current in the primary coil produces a magnetic field
-Field lines interact with secondary coil to induce voltage
-Soft iron core strengthens magnetic field
-Voltage in secondary coil<Voltage in primary coil.

Question 4

Why does an LED flash on and off in an a.c. circuit?

Answer 4

-The direction of the current is always changing direction
-LED doesn’t light up when current is in reverse direction.

Question 5

Why is current not proportional to voltage for a filament lamp?

Answer 5

-The current in the lamp heats up the filament

-Temperature is increased, resistance changes with temp

-Resistance changes gradient of the graph so it isn’t proportional.