P3

Question 1

What is the build up of static caused by?

Answer 1

Transferring electrons.

Question 2

What is the force between two charged objects called?

Answer 2

Electrostatic attraction.

Question 3

How could you test whether an object is charged?

Explain how it works.

Answer 3

Holding a charged rod above small scraps of paper. The charged rod induces a charge in the paper (if it is positively charged), attracting the electrons in paper towards it and repels it if negative.

Question 4

Explain how you could test for charge using a gold leaf electroscope.

Answer 4

Negative charged insulator: charge is transferred to the electroscope, conducted down to the metal stem and gold leaf. This negatively charged both the stem and the gold leaf, causing them to repel against each other.

Question 5

What direction does electric field lines go from?

Answer 5

Positive to negative.

Question 6

State what will happen to the strength of the electric field around a uniformly charged sphere as you move towards the sphere.

Answer 6

The strength of the electric field increases as you move towards the sphere.

Question 7

What is potential difference?

Answer 7

The driving force that pushes the current around.

Question 8

How can you define current?

Answer 8

Current is the rate of flow of electric charge around the circuit.

Question 9

How can you calculate total charge?

Answer 9

Charge = current x time

Question 10

How can you calculate the energy transferred?

Answer 10

Energy transferred = charge x potential difference

Question 11

What is the purpose of an ammeter?

How must it be placed?

Answer 11

It measures the current flowing through components.

It must be placed in series with the component.

Question 12

What does the voltmeter do?

How must it be placed and why?

Answer 12

It measures potential difference.
It must be placed in parallel with the component ;
so it can compare the energy the charge has before and after passing through a component.

Question 13

What is the formula for potential difference?

Answer 13

Potential difference = current x resistance

Question 14

Explain how resistance increase with temperature.

Answer 14

Thermal energy store = kinetic energy store

Particles vibrate more and make it more difficult to transfer electrons through resistors -> resistance increases

Question 15

Why does current only flow in one direction through a diode?

Answer 15

There’s very high resistance in the reverse direction.

Question 16

What is a thermistor and how does it function?

Answer 16

A temperature-dependent resistor.

The resistance drops in hot conditions and goes up in cool conditions.

Question 17

How can thermistors be used in fans ?

Answer 17

Resistance of thermistor increases/ decreases depending on temperature and takes a bigger/ smaller share of the power supply.

Question 18

How do LDRs function in bright conditions?

Answer 18

More light intensity: Resistance of LDR is low and takes less energy for the current to pass through -> low p.d
-brighter light is produced

Question 19

Describe the state of potential difference, current and resistance within a series circuit.

Answer 19

Potential difference is shared.
Current is the same everywhere.
Resistance adds up.

Question 20

Describe the state of potential difference, current and resistance within a parallel circuit.

Answer 20

Potential difference: same
Current: shared
Resistance: dependent on circuit

Question 21

What is power? What is the formula related to it?

Answer 21

The rate of energy transfer.
Energy transferred (J) = power (W) x time (s)

Question 22

How could you calculate power from current and potential difference?

Answer 22

Power = potential difference x current

Question 23

How could you calculate power from current and resistance?

Answer 23

Power = current^2 x resistance