Electricity: EMF and Resistivity

Question 1

What is the equation for resistivity?

Answer 1

ρ = RA / l

Question 2

What is the definition of resistivity?

Answer 2

A measure of the resisting power of a material to the flow of charge.

Question 3

What is resistivity measured in?

Answer 3

Ohmic Meters (Ωm)

Question 4

How does the length of a wire affect resistance?

Answer 4

A longer wire means a higher resistance.

Question 5

How does the cross sectional area of a wire affect resistance?

Answer 5

A wider wire means a lower resistance.

Question 6

How do semiconductors work?

Answer 6

Semi conductors work because electrons are held in bonds in-between the atoms. Once a few electrons have enough thermal energy to escape from these bonds they conduct electric current. As temperature increases, more and more electrons get the ability to conduct electricity. This causes the semiconductor to become a better conductor as temperature increases.

Question 7

What is superconductivity?

Answer 7

A property that causes a material to have zero resistance once it reaches the critical temperature.

Question 8

What are the advantages of superconductors?

Answer 8

You can send current a very long way.
Current doesn’t produce any heat.
Can produce strong magnetic fields.

Question 9

How do we find the total resistance in series?

Answer 9

Rₜ = R₁ + R₂ + R₃ …

Question 10

How do we find the total resistance in parallel?

Answer 10

1/Rₜ = 1/R₁ + 1/R₂ + 1/R₃ …

Question 11

What is Kirchoff’s 1st law?

Answer 11

The sum of the current entering any point in a circuit is equal to the sum of the current leaving that point.
(Total current INTO a junction = Total current OUT OF a junction)

Question 12

In a simple series circuit, how does current behave?

Answer 12

Current will be the same at all points in the circuit.

Question 13

In a parallel circuit, how does current behave?

Answer 13

Current will split at junctions and recombine later.

Question 14

In a simple series circuit, how does potential difference behave?

Answer 14

Voltage is shared between the components in a series circuit.

Question 15

In a parallel circuit, how does potential difference behave?

Answer 15

When voltage reaches a junction, it doesn’t change in either path.

Question 16

How does a multiple cells connected in series behave?

Answer 16

Potential difference increases but current doesn’t change.

Question 17

How does a multiple cells connected in a parallel circuit behave?

Answer 17

Current increases but potential difference doesn’t change.

Question 18

What is Kirchoff’s 2nd law?

Answer 18

The algebraic sum of the directed potential differences in any circuit loop is zero.

Question 19

How do we calculate energy?

Answer 19

E = IVt

Question 20

Name 4 different power equations

Answer 20

P=IV P=W/t P=I²R P=V²/R

Question 21

What is a potential divider circuit?

Answer 21

A circuit used to supply constant or variable potential difference from a power supply.

Question 22

How does a potential divider circuit work?

Answer 22

Two fixed resistors in series can provide a known fraction of a given potential difference. If you change one of the resistors, then you can increase or decrease the voltage.

Question 23

What’s the definition of EMF?

Answer 23

EMF is the power supplied per unit current.

Question 24

What are 2 ways we can calculate EMF?

Answer 24

ε = E/Q OR ε=I(R+r)

Question 25

What’s the definition of internal resistance?

Answer 25

Opposition to the flow of charge within the battery.

Question 26

What is terminal potential difference?

Answer 26

Potential difference measured across the terminals of the power supply. (The output of the cell)

Question 27

How do we calculate terminal potential difference?

Answer 27

V = ε - Ir

Question 28

How do we calculate efficiency?

Answer 28

Efficiency = (Power in Circuit / Power produced by cell) x 100