Resistance

Question 1

Describe voltage, resistance and current in a series circuit.

Answer 1

Voltage=V1+V2, Resistance=R1+R2 and Current is the same throughout.

Question 2

Describe voltage, resistance and current in a parallel circuit.

Answer 2

Voltage is the same on each branch, 1/Resistance= 1/R1+1/R2 and Current= I1+I2.

Question 3

What is the definition of resistance?

Answer 3

The potential difference across the circuit divided by the resulting current through the circuit (R=V/I).

Question 4

What is the potential difference?

Answer 4

The amount of electrical energy to other forms when one coulomb of charge flows between two points.

Question 5

What is a superconductor?

Answer 5

A conductor with zero resistance at very low temperatures.

Question 6

What is the superconducting temperature?

Answer 6

The temperature at which a material, when being cooled, suddenly loses all its electrical resistance, and becomes a superconductor.

Question 7

What causes resistance?

Answer 7

Collisions between free electrons and the positive ions of the metal lattice.

Question 8

What are some uses for superconductors?

Answer 8

Used in nuclear fusion, particle accelerators and MRI scanners.

Question 9

What is a high temperature superconductor?

Answer 9

A superconductor for which the transition temperature is above the boiling point for liquid nitrogen (77K)

Question 10

What are the factors of resistance of a wire?

Answer 10

1. The length- if doubled, resistance doubled
2. The area- if doubled, resistance halved
3. The material of the wire

Question 11

What is Ohms law?

Answer 11

The current flowing through a metal wire at a constant temperature is proportional to the potential difference across it.

Question 12

If resistance increases, what happens to drift velocity?

Answer 12

It decreases.

Question 13

How does resistivity change with different materials?

Answer 13

Conductors have small values of resistivity whereas insulators have high values of resistivity.

Question 14

What are the advantages to using superconductors?

Answer 14

There is no resistance so no heat loss, which means that large currents can be maintained from 0 volts.

Question 15

What are the disadvantages to using superconductors?

Answer 15

Many technical difficulties of achieving and sustaining low temperatures and materials being hard to manufacture and made into wire.

Question 16

What is power and its unit of measurement?

Answer 16

The energy transferred per second (P=W/t) measured in Watts (Js-1).

Question 17

How do we cool superconductors?

Answer 17

Using liquid nitrogen or helium.

Question 18

What is the gradient of a current over voltage graph for a metallic conductor at constant temperature?

Answer 18

A straight line through the origin (Ohms law is obeyed).

Question 19

What is the gradient of a current over voltage graph for a lamp filament?

Answer 19

For low voltages, the graph is straight but the gradient decreases smoothly as the pd increases.

Question 20

What happens to a metal when temperature increases?

Answer 20

The electrons travel faster between collisions and the metal ions vibrate more, which leads to a decreased current for the same voltage and a higher resistance.

Question 21

What are the three equations for power?

Answer 21

P= IV
P= I^2R
P= V^2/R

Question 22

What are the units of resistivity?

Answer 22

Ohm meters (Ωm).

Question 23

What is resistivity?

Answer 23

The resistance of the wire of the material of unit length.