Currents in Electrical Circuits

Question 1

What is a conductor?

Answer 1

A material that an electrical charge can easily pass through. Metals are good conductors thanks to their delocalised electron.

Question 2

What is an insulator?

Answer 2

A material that electrical charges cannot easily move through. Plastics and rubber are good insulators.

Question 3

What is a static charge?

Answer 3

An electric charge that cannot move.

Question 4

Where are static charges usually found?

Answer 4

In insulators

Question 5

How do insulators gain a static charge?

Answer 5

When some insulating materials are rubbed together, electrons are scraped off one onto the other. The one that loses the electrons gains a positive static charge and the one that gains electrons gains a negative static charge.

Question 6

What does it mean if a circuit is complete?

Answer 6

The wire gird from one end of the cell/battery to the other.

Question 7

How must voltmeters be connected to a circuit?

Answer 7

In parallel across the component you are measuring.

Question 8

How must an ammeter be connected to a circuit?

Answer 8

In series

Question 9

What is an electric current?

Answer 9

A flow of electric charge.

Question 10

What side of a cell/battery is positive and which is negative?

Answer 10

The big end is positive and the small end is negative.

Question 11

What way does a charge travel through a circuit?

Answer 11

From positive to negative

Question 12

What is the size of a current? What is it measured in?

Answer 12

The rate of flow of charge. It’s measured in amperes, A.

Question 13

What is the formula for current?

Answer 13

Q
I = —-
t

I = Current (A)

Q = Charge (C - coulombs)

t = Time (secs)

Question 14

What is potential difference?

Answer 14

The driving force that pushes the current round the circuit. It’s the work done per coulomb of charge.

Question 15

What is the formula for potential difference?

Answer 15

W
V = ——
Q

V = Potential difference (V)

W = Work done (J)

Q = Charge (C)

Question 16

What is resistance?

Answer 16

Anything in a circuit that reduces the flow of current.

Question 17

What is resistance measured in?

Answer 17

Ohms, Ω.

Question 18

What is Ohm’s law?

Answer 18

V = I x R

V = Potential difference (V)

I = Current (A)

R = Resistance (Ω)

Question 19

What does a variable resistor do?

Answer 19

You can change its resistance.

Question 20

How would one get negative readings for potential difference?

Answer 20

Switch the way round the wires are connected to the power source. This means that the current will flow in the opposite direction.

Question 21

What does a current-potential difference graph show?

Answer 21

How current varies with potential difference.

Question 22

What do current-potential difference graphs look like for resistors?

Answer 22

Straight line graphs - the current through a resistor is directly proportional to potential difference.

Question 23

What does the current-potential difference graph look like for a filament lamp?

Answer 23

S- shaped. This is because as more current flows through the filament it heats up which makes it more difficult for the current to get through.

Question 24

How does temperature affect resistance?

Answer 24

When a component gets hotter, its ions begin to move which makes it harder for the charge to make it through as resistance increases.

Question 25

Why do most components have a limit to the amount of current they can carry?

Answer 25

Because current increases the temperature of the component meaning eventually its resistance will increase to the point where the current can no longer fit any more charge through.

Question 26

What is the difference between a cell and a battery?

Answer 26

A battery contains multiple cells.

Question 27

What does the symbol for an ammeter look like?

Answer 27

A circle within A in it.

Question 28

What does the symbol for a voltmeter look like?

Answer 28

A circle with a V in it.

Question 29

What does the symbol for a resistor look like?

Answer 29

A hollow rectangle.

Question 30

What does the symbol for a variable resistor look like?

Answer 30

A rectangle with an arrow going through it.

Question 31

What is a diode?

Answer 31

A component that only lets current move freely in one direction through it. This because there's a very high resistance in the other direction.

Question 32

What does the symbol for a diode look like?

Answer 32

A circle with an arrow in it indicating the direction of current flow through it.

Question 33

What does the I-V graph for a diode look like?

Answer 33

It is at 0 for negative values and then goes up very steeply on the positive side.

Question 34

What do LEDs do?

Answer 34

Light Emitting Diodes emit light when a current flows through it in the forward direction. They can be used to indicate the presence of a current in a circuit.

Question 35

What does the symbol for an LED look like?

Answer 35

A circle with an arrow in it indicating the flow of current through it. There are two arrows pointing away from it indicating that it emits light.

Question 36

What three advantages do LEDs have over filament bulbs?

Answer 36

* LEDs have a much longer lifetime * LEDs are much more energy efficient as they don't produce as much waste heat energy * LEDs require a much smaller current so they are cheaper to run

Question 37

What are two disadvantages of LEDs?

Answer 37

* They are much more expensive than filament bulbs | * You often need multiple LEDs to produce the same amount of light as a filament bulb

Question 38

What is the symbol for a filament bulb?

Answer 38

A circle with a cross through it

Question 39

What is an LDR?

Answer 39

A light dependent resistor is a resistor that varies its resistance with light intensity: * In bright light, resistance falls * In darkness, resistance is very high

Question 40

What I the symbol for an LDR?

Answer 40

A circle with a hollow rectangle inside it to represent the resistor. There are two arrows pointing toward the circle to represent the light going in.

Question 41

What are two used of LDRs?

Answer 41

* Streetlights | * Burglar alarms

Question 42

What is an NTC Thermistor?

Answer 42

A resistor whose resistance decreases as temperature increases.

Question 43

What is the symbol for a thermistor?

Answer 43

A resistor with a line going through it. The line is flat on one end.

Question 44

What is a use of thermistors?

Answer 44

Thermostats

Question 45

What is a series circuit?

Answer 45

A circuit in which all the components are connected in line. If one were to be removed the circuit would be broken and it would stop working.

Question 46

How does one work out the potential difference in a series circuit?

Answer 46

Add up the potential differences of all the cells OR add up the potential difference across each component.

Question 47

What is current like in a series circuit?

Answer 47

The same in all parts of the circuit.

Question 48

How does one work out the total resistance of a series circuit?

Answer 48

Add up the individual resistances of each component.

Question 49

What is a parallel circuit?

Answer 49

A circuit in which components have their own branch meaning that if you were to disconnect one of the components it would have no effect on the others.

Question 50

What is potential difference like in parallel circuits?

Answer 50

The same across every branch as each branches potential difference is the same as that of the source.

Question 51

What is the symbol for an open switch?

Answer 51

Two dots with a diagonal line not quite connecting them.

Question 52

What is the symbol for a closed switch?

Answer 52

Two dots connected by a straight line.

Question 53

What is current like in a parallel circuit?

Answer 53

It is split across the branches. To understand the total current you have to add together the current on each branch.

Question 54

What is the symbol for a fuse?

Answer 54

A straight line going through a rectangle.

Question 55

What is the symbol for a motor?

Answer 55

A circle with an M in it.