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

Combine the equations V=W/Q and I=Q/t

Answer 18

V = W/Q -> W = VQ
I = Q/t -> Q=It
W = V(It) - > W = VIt

Question 19

What is the equation and units of power? (Using work done)

Answer 19

P = W/t = VIt/t = IV

Power (Js⁻¹ or W)

Question 20

What is power?

Answer 20

It is the rate at which energy is transferred

Question 21

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

Answer 21

R = V/I
V = IR

Question 22

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

Answer 22

P = IV = (IR)I = I²R

Question 23

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 23

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

Question 24

What is the unit of resistance?

Answer 24

VA⁻¹ = Ω

Question 25

What is resistance?

Answer 25

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

Question 26

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

Answer 26

Constant

Question 27

What is Ohm’s law?

Answer 27

I is proportional to V

Question 28

A conductor that obeys Ohm’s law is…

Answer 28

Ohmic

Question 29

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

Answer 29

G = I/V

AV⁻¹ or S (Siemen)

Question 30

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

Answer 30

G = 1/R

Question 31

Equation for conductance is a parallel circuit (including steps)

Answer 31

G = I/V
G = I₁+I₂ / V
G = I₁/V + I₂/V
G = G₁ + G₂

Question 32

What is the equation for resistance in parallel?

Answer 32

1/R = 1/R₁ + 1/R₂ + …

Question 33

Equation for voltage in series?

Answer 33

V = V₁ + V₂ + …

Question 34

Equation for resistance in series?

Answer 34

R = R₁ + R₂ + …

Question 35

Equation for conductance in series?

Answer 35

1/G = 1/G₁ + 1/G₂ + …

Question 36

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

Answer 36

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

Question 37

What are extensive properties?

Answer 37

Properties that depend on the dimensions or material of the thing (eg, wire)

Question 38

What are intensive or bulk properties?

Answer 38

Properties dependant of dimensions.

Question 39

Are resistance and conductance extensive or bulk properties?

Answer 39

Extensive

Question 40

Give examples of bulk properties

Answer 40

Density, Young’s modulus, Refractive index

Question 41

What is σ?

Answer 41

σ = Electrical conductivity (Sm⁻¹)

Question 42

What is ρ?

Answer 42

ρ = electrical resistivity (Ωm)

Question 43

Conductance = (with sigma)

Answer 43

G = σA / L

Question 44

Resistance = (w/ rho)

Answer 44

R = ρL / A

Question 45

What are the 3 types of material?

Answer 45

Conductor, semiconductor and insulator

Question 46

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

Answer 46

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

Question 47

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

Answer 47

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