12.3- RESISTANCE

Question 1

What is the resistance of a component in a circuit a measure of?

Answer 1

the difficulty of making current pass through the component

Question 2

What is resistance caused by?

Answer 2

repeated collisions between charge carriers in material with each other + with fixed positive ions of material

Question 3

Equation for resistance?

Answer 3

R = V/I

Question 4

What is the unit for resistance?

Answer 4

ohm (Ω)

Question 5

What is a resistor?

Answer 5

component designed to have certain resistance, which is same regardless of current through it

Question 6

Measuring resistance of resistor: what is the ammeter used to measure?

Answer 6

current through resistor

Question 7

Measuring resistance of resistor: how must the ammeter be placed?

Answer 7

in series with resistor

Question 8

Measuring resistance of resistor: why must the ammeter be in series with the resistor?

Answer 8

so same current passes through both the resistor + ammeter

Question 9

Measuring resistance of resistor: what is the voltmeter used to measure?

Answer 9

pd across resistor

Question 10

Measuring resistance of resistor: how must the voltmeter be placed?

Answer 10

in parallel with resistor

Question 11

Measuring resistance of resistor: why must the voltmeter be parallel with the resistor?

Answer 11

so they have the same pd

Question 12

Measuring resistance of resistor: what should NOT pass through the voltmeter?

Answer 12

current

Question 13

Measuring resistance of resistor: why should current not pass through the voltmeter?

Answer 13

otherwise ammeter will not record exact current through resistor

Question 14

Measuring resistance of resistor: in practice, what should the resistor of the voltmeter be like?

Answer 14

infinite resistance

Question 15

Measuring resistance of resistor: what is a variable resistor used to do?

Answer 15

adjust current + pd as necessary

Question 16

Measuring resistance of resistor: why is the variable resistor adjusted in steps?

Answer 16

to investigate variation of current with pd

Question 17

Measuring resistance of resistor: what are the recorded measurements each time the variable resistor is changed, what is done?

Answer 17

recorded current + pd can be plotted on graph of pd against current

Question 18

What is the pd against current graph for a resistor like and what does this mean?

Answer 18

straight line through origin

resistance same regardless of graph as gradient constant

Question 19

What does Ohm’s law state?

Answer 19

pd across metallic conductor proportional to current through it, provided physical conditions don’t change

Question 20

For a conductor of lenghth L and uniform cross-sectional area A, what is its resistance R proportional and inversely proportional to?

Answer 20

proportional to L

inversely proportional to A

Question 21

Equation for resistivity ρ?

Answer 21

ρ = RA/L

Question 22

Unit of resistivity?

Answer 22

ohm metre (Ωm)

Question 23

What is a superconductor?

Answer 23

wire or device made of material that has zero resistivity at + below critical temperature that depends on the material

Question 24

What is the resistance of a wire/device like below the critical temperature?

Answer 24

zero resistance

Question 25

When a current passes through a superconductor what happens?

Answer 25

no pd across it as its resistance is zero, so current has no heating effect

Question 26

When does a superconductor lose its superconductivity?

Answer 26

if its temp raised above its critical temp

Question 27

What is a high-temperature superconductor?

Answer 27

any material with critical temp above 77K

Question 28

What are superconductors used to make?

Answer 28

high-power electromagnets that generate very strong magnetic fields in devices i.e. MRI scanners + particle accelerators

Question 29

What are the strong magnetic fields of superconductors also used in?

Answer 29

development of new applications i.e. lightweight electric motors + power cables that transfer electrical energy without energy dissipation