Unit 2.2)Resistivity

Question 1

What is the definition of potential difference and What is it measured in?

Answer 1

The work done moving a unit charge between two points in a circuit.
V=W/Q.
V(potential difference) W(work done)
Q(Charge)
Measured in(V) where V = J C^-1.

Question 2

What is resistance?

Answer 2

A measure of how difficult it is for current to flow through an appliance.
measured in ohms(Ω) where Ω =V A^-1.

Question 3

What is meant by an ohmic conductor?

Answer 3

A conductor that obeys ohms law, meaning current is directly proportional to potential difference providing the temperature remains constant.

Question 4

,Ohms law?

Answer 4

V=IR
R is constant for all values of V and I.
The electrical current between two points is directly proportional to the voltage accross the two points, provided the temperature remains constant.

Question 5

What does the gradient of a current-potential difference graph represent?

Answer 5

1/R
Because the gradient = rise in current/change in potential difference i.e. gradient = I/V.
As resistance= V/I, the gradient = 1/R.

Question 6

What graph represents an ohmic conductor?

Answer 6

A current voltage graph which its line has a constant gradient and passes through the origin. Which shows that voltage is directly proportional to current.

Question 7

Shallower gradient higher_____?

Answer 7

higher resistance, as gradient =1/R is a smaller value for the gradient.

Question 8

What does a filament lamp curve look like on a current potential - difference graph?

Answer 8

Look at this https://www.savemyexams.com/a-level/physics/ocr/17/revision-notes/4-electrons-waves–photons/4-2-resistance–resistivity/4-2-2-ohms-law–i-v-characteristics/.

Question 9

Why does the current increasing on a filament lamp cause an increase in the resistance?

Answer 9

As current flows through the lamp, electrical energy is converted to heat energy so the metal ions vibrate with increased amplitude impeding the movements of electrons through the lamp as they collide with the ions(resistance has increased).

Question 10

What is resistivity?

Answer 10

The resistance of a 1m cylinder with a cross sectional area of 1m^2
p= RA/L
p=resistivity, R=resistance
A=cross sectional area, m^2 L=length, m

Question 11

What is power?

Answer 11

The rate of energy transfer. (The rate at which work is being done.)

Question 12

What is a super conductor?

Answer 12

A material that, when cooled below its critical temperature, has a resistivity of zero.

Question 13

State 2 applications of superconductors?

Answer 13

1.Power cables, which would reduce energy loss through heating to zero during transmission.
2.Strong magnetic fields, which would not require a constant power source. These could be used in maglev trains, where there would be no friction between the train and rail. They could also be used in certain medical applications.

Question 14

What is resistivity?

Answer 14

The resistivity is a property of a metal which shows how easy or difficult it is for current to flow in the material(at a specific temperature.
p=RA/L
P=resistivity, R=resistance, A=cross-sectional area, L=length.

Question 15

True or false? The resistivity of both metals and semiconductors increases with temperature? if yes or no why?

Answer 15

False.
Collisions between free electrons and ions in metals increase the random vibration energy of the ions, so the temperature of the metal increases.
Some semiconductors get less resistive as temperature increases, because supplying energy actually causes more charge carriers to be released, so current can flow more easily.

Question 16

what is superconductivity?

Answer 16

Superconductivity is when a material conducts with zero resistance. A material will begin to do this when it is cooled to below a certain temperature. Not all materials can do this however.

Question 17

What is the transition temperature?

Answer 17

The temperature below which a superconductor must be cooled in order to have zero resistance is called the transition temperature.

Question 18

When do metals show superconductivity?

Answer 18

Most metals do show superconductivity and will have transition temperatures a few degrees higher then absolute zero.

Question 19

Describe some uses of superconductivity?

Answer 19

Superconductors can be used as magnets to make vehicles such as trains float.
MRI scanners use superconducting magnets to expose the human body to a strong magnetic field.
Superconducting magnets are often used in particle accelerators to alter the paths of subatomic particles.

Question 20

Power equation(s).

Answer 20

P=IV
P=power
I=current
V=voltage
Units watts(W)

P=V^2R
when you know Voltage(v) and Resistance(R).

P=I^2R
When you know current(I) and Resistance(R).

Question 21

What gives rise to electrical resistance?

Answer 21

Collisions between free electrons and ions gives rise to electrical resistance, and electrical resistance increases with temperature?

Question 22

High temperature super conductors?

Answer 22

Some materials have transition temperatures above the boiling point of nitrogen these are high temperature superconductors.