Electricity 4.2 Electrical Quantities

Question 1

Where are electric fields found?

Answer 1

Around every electric charge.

Question 2

What is an electric field?

Answer 2

Region where a force acts on an elctric charge

Question 3

Objects with the same charge…

Answer 3

…repel.

Question 4

Objects with opposite charges…

Answer 4

…attract.

Question 5

What is charging?

Answer 5

The addition or removal of electrons from a material.

Question 6

Describe charging by induction?

Answer 6

Place positively/negatively charged rod close to surface of conductor
Touch conductor w/ finger
Remove charged rod

Question 7

What is a conductor?

Answer 7

A conductor is a material which can conduct electricity; electrons are able to flow through it.

Question 8

What is an insulator?

Answer 8

An object which does not conduct electricity. Electrons cannot flow through the material

Question 9

How is static electricity produced?

Answer 9

When two insulators are rubbed together, transferring electrons, to form a positive and a negative charge.

Question 10

What is an electric current?

Answer 10

Current is the rate of flow of charge in an electric circuit.

Question 11

What is required in order for charge to flow?

Answer 11

• A potential difference
• A closed circuit

Question 12

Describe the value of current across a series & parallelcircuit

Answer 12

Series: same everywhere (I1=I2)

Parallel: shared between branches (Isource = I1+I2+…)

Question 13

Give an equation linking charge and current, giving SI units

Answer 13

charge (C) = current (A) x time (s)

Question 14

How is current measured?

Answer 14

Using an ammeter, wired in series to the circuit.

Question 15

What is conventional current?

Answer 15

Conventional current (used in circuit diagrams etc.) represents the flow of positive charge; it flows in the opposite direction to the flow of electrons.

Question 16

What is EMF?

Answer 16

Electromotive force (the voltage supplied by a power source)
Energy supplied in driving coulomb (unit charge) around circuit

Question 17

What are the units of EMF?

Answer 17

Volts, V.

Question 18

What are the units of potential difference?

Answer 18

Volts, V.

Question 19

Define potential difference

Answer 19

The work done per unit charge flowing between any two points.

Question 20

How is potential difference measured?

Answer 20

Using a voltmeter, wired in parallel.

Question 21

Give an equation linking current and potential difference

Answer 21

V=IxR
p.d. (V) = current (A) x resistance (omhs)

Question 22

How does resistance affect the current flowing through a circuit?

Answer 22

The larger the total resistance in the circuit, the smaller the current will be.

Question 23

Describe an experiment to investigate the resistance of a wire.

Answer 23

• Use a length of wire connected to an ammeter (in series), a voltmeter (in parallel) and a power supply
Connect two crocodile clips to the wire, one at each end, and record the current and voltage
• Vary the length of the wire (moving one of the clips), recording V and I
• Plot a graph of V against I; the gradient = resistance of wire

Question 24

Describe current voltage graph of a resistor

Answer 24

If V increased, I increases (directly proportional)

Question 25

Describe current voltage graph of filament lamp

Answer 25

As V increases so does I untill a certain point where graph plateaus and I no longer increases. As I increases in filament lamp, so does temp So electrons + ions vibrate more & collide more increasing resistance

Question 26

How does resistance relate to the length of a wire?

Answer 26

Resistance increases with length. They are directly proportional

Question 27

How does resistance relate to the cross sectional area of a wire?

Answer 27

Resistance decreases as cross sectional area increases (they are inversely proportional).

Question 28

How is energy transferred in a circuit?

Answer 28

From the battery/power source to the circuit components, and dissipated into the surroundings as heat.

Question 29

What factors affect the energy transferred when charge flows through a component?

Answer 29

• Amount of charge • The potential difference across the component

Question 30

Give an equation linking power and potential difference

Answer 30

power (W) = current (A) x p.d. (V)

Question 31

Give an equation linking power and energy

Answer 31

power (W) = energy (J) / time (s) This means that E = V x I x t