Electricity - Paper 1

Question 1

Draw the circuit symbol for a lamp

Answer 1

an X in a circle

Question 2

Draw the circuit symbol for a diode

Answer 2

An arrow head in a circle

Question 3

Draw the circuit symbol for a resistor

Answer 3

A rectangular box

Question 4

Draw the circuit symbol for a variable resistor

Answer 4

A rectangular box with a diagonal arrow

Question 5

Draw the circuit symbol for an LED

Answer 5

Same as a diode with 2 arrows points away

Question 6

Draw the circuit symbol for a fuse

Answer 6

A rectangular box with a horizontal one running through it

Question 7

Draw the circuit symbol for a voltmeter

Answer 7

V in a circle

Question 8

Draw the circuit symbol for an ammeter

Answer 8

A in a circle

Question 9

Draw the circuit symbol for a thermistor

Answer 9

a rectangular box with a diagonal line through it

Question 10

Draw the circuit symbol for an LDR

Answer 10

A rectangular box in a circular with 2 arrows pointing towards it

Question 11

Define Current

Answer 11

Flow of charge (electrons) measured in amps (A)

Question 12

State the equation that links charge, current and time.

Answer 12

Charge (C)= Current (A) x time (s)

Q = It

Question 13

What are the units of charge

Answer 13

Coulombs (C)

Question 14

What is the relationship between current and resistance?

Answer 14

They have an inverse relationship. As resistance increases, current decreases and vice versa

Question 15

State the equation that links potential difference, current and resistance

Answer 15

Potential difference (V) = Current (A) x resistance (ohms)

V = IR

Question 16

State the units of potential difference

Answer 16

Volts (V)

Question 17

State the units of resistance

Answer 17

Ohms

Question 18

State the relationship between the length of wire and its resistance.

Answer 18

As the length of the wire increases the resistance increases. They are directly proportional. If the lenght of wire doubles then the resistance will double.

Question 19

As more resistors are added in series what happens to the total resistance.

Answer 19

Total resistance increases (Rt = R1 + R2 + …..) as the current has to flow through every resistor.

Question 20

As more resistors are added in parallel what happens to the total resistance.

Answer 20

As more resistors are added in parallel then the total resistance decreases. This is because the electrons have more paths they can take back to the battery.

Question 21

State ohms law

Answer 21

Current is directly proportional to potential difference at a constant temperature. This means resistance remains constant.

Question 22

Do the following components obey ohms law:

resistor?

Lamp?

Diode?

Answer 22

Resistor - yes

Lamp - No

Diode - No

Question 23

Sketch the I/V graph for a resistor

Answer 23

A straight line through the origin (current and potential difference are directly proportional - an ohmic conductor)

Question 24

Sketch the I/V graph for a bulb

Answer 24

It starts off as a straight line through the origin but the the current levels offs so the graph curves. Non ohmic conductor as current is not proportional to potential difference

Question 25

How does the resistance of a lamp change as it heats up?

Answer 25

As temperature increases resistance increase. Atoms/ions have more energy so vibrate more taking up more space making it harder for electrons to travel down the wire. This causes the I/V graph for a bulb to level off.

Question 26

Sketch the I/V graph for a diode

Answer 26

Current can only flow in one directions. So zero current in the negative direction but in the positive direction current increases just after the origin. Non ohmic conductor

Question 27

State the relationship between temperature and resistance for a thermistor

Answer 27

As temperature increases resistance decreases.

Question 28

State some uses of thermistors

Answer 28

In thermostats to turn circuits on/off if they get too hot to cold e.g. in an iron, oven, central heating, hair straighteners etc

Question 29

State the relationship between temperature and light intensity for a LDR

Answer 29

As light increases increases, resistance decreases

Question 30

State some uses of LDRs

Answer 30

In circuits to switch lights on when it gets dark e.g. street lights

Question 31

state the rules for current, potential difference and resistance in a series circuit

Answer 31

1. Current - same flowing through each component 2. Potential difference - the p.d. of the power supply is shared between the other components 3. Resistance - the total resistance increases as more components are added. the total resistance is the sum of all the individual components resistance

Question 32

state the rules for current, potential difference and resistance in a parallel circuit

Answer 32

1. current - splits up but the total current stays the same 2. Potential difference - across each brach is the same as from the battery 3. Resistance - decreases as more branches are added. the electrons have more choice of paths to take.

Question 33

What happens when electrical current flows through a resistor?

Answer 33

Electrical energy is transformed into heat energy

Question 34

What is a short circuit?

Answer 34

An electrical circuit that allows current to travel along a paths with no or very low resistance Resistance low = current very high. This will cause the battery to overheat

Question 35

Why do lamps blow when they have just been turned on?

Answer 35

The lamp is cold so it has low resistance, this means a high current flows - sometimes enough to melt the wire in the bulb

Question 36

In a potential divider, what happens to the potential difference from the battery when two components have equal resistance?

Answer 36

They share the potential difference from the battery equally.

Question 37

In a potential divider, a current passes through a resistor then through a thermistor. How does the current and voltage across each component change as temperature increases?

Answer 37

The thermistor heats up. The resistance of the thermistor decreases, and then takes a smaller share of input voltage from the battery (voltage decreases). As the input from the battery is constant the voltage increases across the fixed resistor. As the resistance deceases the current decreases.

Question 38

In a potential divider, a current passes through a resistor then through an LDR. How does the current and the voltage across each component change as light intensity increases?

Answer 38

If light intensity increases the resistance of the LDR decreases. The LDR will take a smaller share of the input voltage (voltage decreases). As the input voltage from the battery is fixed the voltage across the fixed resistor must increase. If resistance decreases then the current will increase.