sp10

Question 1

in a circuit with a heater and variable resistor, why is the total energy supplied by the battery different to the energy transferred by the heater?

Answer 1

there is the same current in the wires, energy is lost in the wires as heat

Question 2

bright sunlight - 0.039 A
cloudy skies - 0.028 A
why are the current readings different?

Answer 2

resistance changes, more resistance in the dark

Question 3

why does electric current in a resistor make the resistor heat up?

Answer 3

energy is transferred, collisions of electrons

Question 4

what changes the size of an alternating voltage?

Answer 4

a transformer

Question 5

how can LDRs and thermistors control the current?

Answer 5

LDR:
bright, low resistance, high current
dark, high resistance, low current

thermistor:
high temp, low resistance, high current
low temp, high resistance, low current

Question 6

why is only some electrical energy transferred to light in a lamp?

Answer 6

thermal energy is produced in the lamp

Question 7

transformers?

Answer 7

only changes a.c.

Question 8

what is current?

Answer 8

rate of flow of charge

Question 9

how do transformers improve efficiency

Answer 9

step-up transformers, increase voltage, reduce current, reduce thermal energy loss

Question 10

why does a coil in a motor become warm?

Answer 10

wires have resistance, current is due to the movement of electrons through a lattice of positive ions, collisions between electrons and ions transfer energy from electrons to the lattice