P2 - Electricty

Question 1

Electrical Current

Answer 1

The flow of electrical charge, it’s measured in amps (A)
Charge = current x time
Q =It
There are two types: direct and alternating
In a direct current, the flow of electrons is consistently in one direction around the circuit
In an alternating current, the direction of the electron flow continually reverses

Question 2

Potential Difference

Answer 2

The energy given to the charge carriers in a circuit, it’s measured in volts (V)
Potential difference = current x resistance
V = IR
To measure potential difference across a component, a voltmeter is placed in parallel with the component

Question 3

Resistance

Answer 3

The opposition in an electrical component to the movement of electrical charge through it, it’s measured in ohms (Ω)
Potential difference = current x resistance
V = IR

Question 4

Investigating the Factors Affecting Resistance

Answer 4

1) connect the 1.5 V cell, ammeter, voltmeter and thin resistance wire in a circuit, with the crocodile clips on the resistance wire 100cm apart
2) record the reading on the ammeter and voltmeter
3) repeat steps 1 and 2 decreasing the distance between the crocodile crocodile clips by 10cm each time until a minimum length of 10cm is reached
4) use the results to calculate the resistance of each length of wire using R = V ÷ I

Question 5

Investigating Current

Answer 5

1) connect a battery, ammeter, resistor with a voltmeter parallel to it and a variable resistor in a circuit, and set the power supply to 0
2) record the reading on the ammeter and the voltmeter
3) alter the potential difference using the variable resistor
4) record the new reading on the ammeter and voltmeter
5) repeat steps 3 and 4, each time increasingly the potential difference by a set amount
6) repeat the experiment but replace the resistor with a bulb or diode

Question 6

Series Circuits

Answer 6

A circuit where one component follows directly from another/is all one loop. In a series circuit, current is consistent across each component or part of the circuit (I1 = I2) whereas potential difference is split across components (V = V1 + V2). If resistors are connected in series, the current must flow through both, meaning the resistances are added together (R = R1 + R2)

Question 7

Parallel Circuit

Answer 7

A circuit where components are connected alongside on another, forming extra loops. In a parallel circuit, current is split across components or parts of the circuit (I = I1 + I2) whereas potential difference is the across each component (V1 = V2). If resistors are connected in parallel, the current is divided between them, so the overall resistance is reduced

Question 8

Investigating Resistor Networks

Answer 8

1) set up a series circuit with a battery, switch, ammeter and a resistor with a voltmeter connected in parallel
2) record the voltmeter and ammeter readings and calculate the resistance
3) change the resistor and repeat step 2
4) repeat step 2 but this time with two resistors (in series)
5) then arrange the resistors in parallel and repeat step 2 again

Question 9

Ohm’s Law

Answer 9

If the resistance across a component is constant, current is directly proportional to the potential difference, e.g. a resistor kept at a constant temperature

Question 10

Changes in Resistance: Current

Answer 10

When electrons flow through a resistor, they collide with the atoms in the resistor:
- current increases, electrons have more energy, more energy transferred to atoms which vibrate more, harder for electrons to flow through resistor so resistance is increased and current decreases
- current decreases, opposite process occurs, and resistance decreases, and so current increases

Question 11

Changes in Resistance: Temperature

Answer 11

With a normal resistor: temperature increase = resistance increase
With thermistor: temperature increase = resistance decrease

Question 12

Changes in Resistance: Length

Answer 12

Greater length = greater resistance as electrons have to flow through more resistor atoms

Question 13

Changes in Resistance: Light

Answer 13

Light dependent resistor: greater light intensity = lower resistance

Question 14

Mains Electricity

Answer 14

An alternating current supply with a frequency of 50Hz and voltage of 230V

Question 15

Plug Sockets

Answer 15

Made up of three parts:
- live wire (brown, 230V, carries alternating potential difference from supply)
- neutral wire (blue, 0V, completes the circuit)
- earth wire (green and yellow stripes, 0V, safety wire - only carries current if there’s a fault)

Question 16

Power

Answer 16

Energy transferred per second. It’s directly proportional to current and voltage, and power loss is proportional to resistance and to the square of the current
Power = current² x resistance
P = I²R
Power = current x potential difference
P = IV
Power = energy transferred ÷ time
P = E ÷ t
Energy transferred = charge x potential difference
E =QV

Question 17

National Grid

Answer 17

A system of cables and transformers linking power stations to consumers across the UK:
Power station > step-up transformer > power cables > step-down transformer > consumer

Question 18

Transformers

Answer 18

Step-up transformers: increase voltage and decrease current from power station to national grid so less energy is lost
Step-down transformers: decrease voltage and increase current from national grid to consumers so it is safer

Question 19

Electric Fields

Answer 19

Shown by diagrams, where arrows point in direction a positive charge would move. The stronger the charge, the more field lines present and the stronger the force felt and being closer to the charge means a stronger force is felt