P4 and P5

Question 1

What is the function of a cell?

Answer 1

-Pushes electrons around a complete circuit.

Question 2

What is the equation for the total resistance in a series circuit?

Answer 2

R total= R1 + R2 +R3..

-The total resistance of two or more components in series is equal to the sum of the resistance of each component

Question 3

What is the function of a switch?

Answer 3

-Enables the current in a circuit to be switched on or off

Question 4

What is the function of an indicator (bulb)?

Answer 4

-Designed to emit light as a signal when a current passes through it

Question 5

What is the function of a diode?

Answer 5

-Allows current through in one direction called forward direction

Question 6

What is the function of a light-emitting diode(led)?

Answer 6

-Emits light when a current passes through it

Question 7

What is the function of an ammeter?

Answer 7

-Used to measure electric current

Question 8

What is the function of a fixed resistor?

Answer 8

-Limits the current in a circuit

Question 9

What is the function of a variable resistor?

Answer 9

-Allows the current to be varied

Question 10

What is the function of a fuse?

Answer 10

-Designed to melt and therefore ‘break’ circuit if the current through it is greater than a certain amount

Question 11

What is the function of a heater?

Answer 11

-Transfers the energy from an electric current to heat the surroundings

Question 12

What is the function of a voltmeter?

Answer 12

-Used to measure potential difference

Question 13

What is an electric current(I)?

Answer 13

• A flow of charge

- measured in amperes(A)

Question 14

What is a battery?

Answer 14

-Consists of two or more cells

Question 15

What does Ohm’s law state?

Answer 15

• That the current flowing through a resistor at a constant temperature is directly proportional to potential difference across the resistor
  e. g. if you double the voltage, the current also doubles.
• Reversing the potential difference across a resistor reverses the current through it

Question 16

What happens if a filament lamps resistance increases?

Answer 16

-The temperature increase

Question 17

direct current

Answer 17

• flows in one direction only

e. g. battery in a torch

Question 18

alternating current

Answer 18

-repeatedly reverses direction of flow. flows one way then the other in successive cycles
e.g. light switch at home
-frequency is number of cycles passed through each second
-to measure frequency use:
frequency= 1/time taken for 1 cycle

Question 19

mains circuit

Answer 19

• every mains circuit has a live wire and a neutral wire

- some appliances have a earth wire this is needed if the appliance has a metal casing.

Question 20

live wire

Answer 20

• carries a current that alternates between positive and negative values
• bottom left on a plug socket
• coloured brown

Question 21

neutral wire

Answer 21

• has a voltage which stays close to zero
• bottom right on a plug socket
• coloured blue

Question 22

earth wire

Answer 22

• if appliance has a metal casing it needs to be earthed
• if there is a fault a large current flows to the earth wire + overloads the fuse
• coloured stripes of green and yellow
• connected to the longest pin in a plug(top pin)

Question 23

cables and plugs

Answer 23

• sockets + plugs are made of stiff plastic materials because plastics a good insulator
• a mains cable is made up of two or three insulated copper wires surrounded by an outer layer of flexible plastic material

Question 24

What are the current, potential difference and resistance in parallel circuits?

Answer 24

• The total current through the whole circuit is the sum of the currents through the separate branches
• Potential difference across each component is the same

Question 25

What are the current, potential difference and resistance in series circuits?

Answer 25

- Current is the same in each component - Total potential difference is shared between the components - Total resistance is the sum of the individual resistances

Question 26

What is a battery?

Answer 26

-Consists if two or more cells connected together

Question 27

What is the size of an electric current?

Answer 27

- The rate of flow of charge | - The flow of charge per second

Question 28

What does a circuit diagram show?

Answer 28

-How components are connected together

Question 29

What is electric charge measured in?

Answer 29

Couloumbs (C)

Question 30

What is electric current measured in?

Answer 30

Amperes (A) or Amps

Question 31

What is the equation for the electric current of a circuit?

Answer 31

``` Charge flow,Q=Current,I x Time taken,T Q= I x T Or Current= Charge flow /Time taken I= Q/T Or Time taken= Charge flow/Current T=Q/I ``` Q= Couloumbs(C) I=Amperes(A) T=Seconds(S)

Question 32

What is potential difference?

Answer 32

-The difference of electrical potential between two points

Question 32

What is resistance and what are its units?

Answer 32

- a measure of the difficulty to pass an electric current and its electrons through that conductor - Unit of resistance is the ohm

Question 32

What is the equation for the potential difference across a component?

Answer 32

Potential difference across a component, V = energy transferred, E/ Charge, Q ``` V = Volts(V) E = Joules(J) Q = Coulombs(C) ```

Question 33

What is the equation for resistance?

Answer 33

Resistance, R = potential difference, V/ Current, I ``` R = Ohms V= Volts (V) I = Amperes (A) ```

Question 34

What is an Ohmic conductor?

Answer 34

- A resistor at constant temperature | - As current is directly proportional to potential difference

Question 35

A current-potential difference graph for a diode:

Answer 35

- Diode has low forward resistance - Diode has a very high reverse resistance. so current can only flow in other direction - Doesn’t follow Ohm’s law

Question 36

A current-potential difference graph for a filament lamp:

Answer 36

- The resistance increases as the current increases, so the resistance increases as the filament temperature increases - Current is not directly proportional to the potential difference across it - Doesn’t follow Ohm’s law

Question 37

A current-potential difference graph for a resistor:

Answer 37

- The current flowing through a resistor at a constant temperature is directly proportional to the potential difference across it - This follows Ohm’s law

Question 38

Thermistor’s resistance:

Answer 38

-A thermistor’s resistance decreases if its temperature increases

Question 39

LDR’s resistance:

Answer 39

-An LDR’s resistance decreases if the light intensity on it decreases

Question 40

What does adding more resistors in series do?

Answer 40

-Adding more resistors in series increases the total resistance because the current through the resistors is reduced and the total potential difference across them is unchanged

Question 41

What does adding more resistors in parallel do?

Answer 41

-Adding more resistors in parallel decreases the total resistance because the total current through the resistors is increased and the total potential difference across them is unchanged

Question 42

What is the total resistance of two or more components in parallel?

Answer 42

-The total resistance of two or more components in parallel is less than the resistance of the resistor with the least resistance

Question 43

What is the equation for current through a resistor in a parallel circuit?

Answer 43

Current, I = Potential difference, V/Component resistance, R I=V/R Or Potential difference, V = Current, I x Resistance, R ``` I = Amperes(A) V = Volts (V) R = Ohms ```