Chapter 3

Question 1

A flow of charged particles produces an [ ]

Answer 1

Electric current

Question 2

Each electron has the same [ ] measured in [ ]

Answer 2

Charge (Q)

Coulombs (C)

Question 3

What equation links I, Q and t?

Answer 3

I = ΔQ/Δt

Question 4

Current is measured in [ ]

Answer 4

Amperes (A)

Question 5

The [ ] is the same at all points along the stream of [ ]

Answer 5

current

charged particles

Question 6

Describe current when a wire forks

Answer 6

The current splits

I = I₁+I₂

Question 7

What is Kirchhoff’s first law?

Answer 7

That the current at a junction must add up

Question 8

When will charges move?

Answer 8

When attracted by charges of the opposite sign or when repelled by charges of the same sign

Question 9

What happens inside a battery cell?

Answer 9

Chemical reactions produce an electrical potential energy difference between the 2 terminals resulting in a +ve charged terminal and a -ve charged terminal

Question 10

If the poles of the cell are joined by a [ ], charges will flow

Answer 10

conducting path

Question 11

Describe which charges flow in which directions

Answer 11

+ve charges flow from the +ve pole to the -ve pole, and -ve charges move the other way

Question 12

Which charges are more likely in circuits?

Answer 12

As metals contain free electrons, which are -ve charged, the movement of -ve charges is more usual in a circuit

Question 13

When charges move between 2 points in a circuit, their [ ] changes by amount ΔE

Answer 13

electrical potential energy

Question 14

What is the equation of voltage (Using E,Q and W)?

Answer 14

V = ΔE / Q = W/Q

Question 15

The P.d between ends of a wire will [ ] the free elctrons

Answer 15

Accelerate

Question 16

What obstructs the free electrons moving down a wire?

Answer 16

By their interactions with the +ve ion cores of the metal atoms, so they don’t gain kinetic energy

Question 17

What does the p.d lost by electrons obstructing do? What’s this called?

Answer 17

The p.d lost does work on the wire, heating it

This ‘wasted’ energy is called dissipation and the process is called ‘Joule Heating’

Question 18

What is power?

Answer 18

It is the rate at which energy is transferred

Question 19

What is the equation for resistance (voltage and current)?

Answer 19

R = V/I
V = IR

Question 20

What is the equation for power (w/ resistance)?

Answer 20

P = IV = (IR)I = I²R

Question 21

When there is a constant current in a conductor, the forward push of the moving charges from the p.d, between the ends of the conductor is balanced by the …

Answer 21

…obstructing effect of the atoms in the conductor interacting with the charges.

Question 22

What is the unit of resistance?

Answer 22

VA⁻¹ = Ω

Question 23

What is resistance?

Answer 23

Is a measure of how difficult it is to get the current through the component

Question 24

For most metals at a constant temp. the resistance is [ ]

Answer 24

Constant

Question 25

What is Ohm’s law?

Answer 25

I is proportional to V

Question 26

A conductor that obeys Ohm’s law is…

Answer 26

Ohmic

Question 27

What is the equation for conductance (With Voltage)?Units?

Answer 27

G = I/V

AV⁻¹ or S (Siemen)

Question 28

What is the equation of conductance (w/ Resistance)?

Answer 28

G = 1/R

Question 29

What is the equation for resistance in parallel?

Answer 29

1/R = 1/R₁ + 1/R₂ + …

Question 30

Equation for voltage in series?

Answer 30

V = V₁ + V₂ + …

Question 31

Equation for resistance in series?

Answer 31

R = R₁ + R₂ + …

Question 32

Equation for conductance in series?

Answer 32

1/G = 1/G₁ + 1/G₂ + …

Question 33

From a p.d - current graph, how can you tell if the component is ohmic?

Answer 33

If the line is straight (proportional) then the component is ohmic, otherwise non-ohmic.

Question 34

What are extensive properties?

Answer 34

Properties that depend on the dimensions or material of the thing (eg, resistance or conductance).

Question 35

What are intensive or bulk properties?

Answer 35

Properties not dependant of dimensions. (eg Young’s Modulus).

Question 36

What is σ?

Answer 36

σ = Electrical conductivity (Sm⁻¹)

Question 37

What is ρ?

Answer 37

ρ = electrical resistivity (Ωm)

Question 38

Conductance = (with sigma)

Answer 38

G = σA / L

Question 39

Resistance = (with rho)

Answer 39

R = ρL / A

Question 40

What are the 3 types of material?

Answer 40

Conductor, semiconductor and insulator.

Question 41

How can you measure the resistivity/conductivity of an insulator?

Answer 41

You need a tiny value of L, a large value of A, a large p.d, and a very, very sensitive ammeter.

Question 42

How can you measure the resistivity/conductivity of an metal?

Answer 42

You need a large L and a very small A, and you must be aware of the complications cause by I²R heating of the wire and systematic errors such as p.d drops in places other than across the conductor in question

Question 43

What happens when semiconductors are heated?

Answer 43

The proportion of atoms that are ionised increases greatly. thus increasing the number of charge carriers and therefore the overall conductivity.

Question 44

What happens to the conductivity of LDRs/Thermisters when light/temperature is raised.

Answer 44

Increases as the increase in light/temperature liberates electrons.

Question 45

What is Kirchhoff’s second law?

Answer 45

e.m.f=sum of all p.d.s across the resistances of the circuit.