Unit 2 - Resistance

Question 1

What is potential difference

Answer 1

The energy transfered from electrical potential energy to another form of energy for each unit of charge that passes

(Its converted into other forms of energy because its the voltage that goes through a component, for each unit of charge that passes)

Question 2

What is potential difference messured in

Answer 2

Volts (V)

Question 3

What is electro motive force

Answer 3

energy that changes to electrical potential energy per charge passing through the source.

Question 4

what is ohms law

Answer 4

that the potential difference across a component is directly proportional to the current through it. Providing that the temperature stays the same (V=IR)

Question 5

What is resistance

Answer 5

A measure of how difficult it is for current to flow (measured in ohms)

Question 6

What does higher resistance mean for the potenial difference

Answer 6

higher resistance means that a larger potental difference is required to produce a current.

Question 7

Why does resistance occur

Answer 7

Because of the collisions between the free electrons and the ions.

Question 8

How does resistance rise approximately linearly with temperature

Answer 8

if you increase the temperature of a conductor, the ions move around more energetically so more energy is transfered from electrons to ions. So it is harder for electrons to flow, so resistance rises.

Question 9

What happens when free electrons and ions collide in a metal

Answer 9

When they collide, it increases the kinetic energy (in vibrations) of the ions, so it increases the temperature of the metal.

Question 10

What is meant by ohmic and non-ohmic

Answer 10

Ohms law states that R is constant for all values of V and I, conductors that have this property are ohmic, conductors which don’t are non-ohmic

Question 11

What is resistivity

Answer 11

A measurement of how much a material resists the flow of current

Question 12

Unit of resistivity?

Answer 12

Ohm meter

Question 13

What is I-V characteristics

Answer 13

The plot of current against voltage is called an I-V characteristic

Question 14

Describe I-V graph for a filament lamp

Answer 14

The line is curved, this is because the resistance increases at higher points of voltage. As potental difference is applied to the lamp, a current flows, causing the lamp to light, this current flow means that some heat energy is dissipated in the filament, causing the filament to heat up, so resistance increases. Doesn’t obey ohms law because temperature doesn’t stay the same.

Question 15

Describe I-V graph for a resistor/metal wire at constant temperature

Answer 15

Current is directly proportional to the potential difference, line is straight, and so resistance is constant as current increases. Therefore it is an ohmic conductor because the temperature is constant.

Question 16

What is superconductivity?

Answer 16

When a material conducts with zero resistance, because it has been cooled to below a certain temperature.

Question 17

What is transition temperature?

Answer 17

The temperature below which a superconductor must be cooled, in which suddenly the resistance drops to zero and the material becomes a superconductor

Question 18

How is superconductivity used in maglev trains

Answer 18

using superconductors to produce a strong magnetic field which makes the train levitate off the track, by doing this there is no resistance between the train and the track, and so the train can reach really high speeds.

Question 19

How is superconductivity used in MRI scanners

Answer 19

MRI scanners are used for medical diagnosis, using a superconductor, a strong magnetic field aligns hydrogen atoms in the body. Radio waves are absorbed and emitted by these hydrogen atoms and an image of the body can be produced.

Question 20

How is superconductivity used in Particle Accelerators

Answer 20

Superconductors produce a magnetic field which keep the particles in a beam and steer them aroind the circular detector.

Question 21

Name 3 uses of Superconductors

Answer 21

-Maglev Trains
-MRI Scanners
-Particle Accelerators

Question 22

Equation for work done (and units)

Answer 22

Work done(J) = voltage(v) x charge(c)

Question 23

Alternate unit for voltage rather than V

Answer 23

JC⁻¹

Question 24

What is equation for energy

Answer 24

E = power x time
E = Voltage x Current x time

(Since power = IV

Question 25

Define power

Answer 25

Rate of doing work (Watts or sometimes Js⁻¹)

Question 26

Why is superconductivity achieved?

Answer 26

When it is cooled to a certain temperature, the atoms/ions in the metal vibrate less, so less collisions. And as temperature decreases electrons can move around closer to each other and sometimes form pairs called cooper pairs.

Question 27

What is the transition temperature usually for metals

Answer 27

A few degrees above absolute zero (absolute zero is in kelvin, equals to -273 celcius)

Question 28

What is high temperature superconductors

Answer 28

Certain materials with transition temperatures above 77 Kelvin (-196 Celsius)