PHYSICS RESISTANCE

Question 1

What is the definition for potential difference?

Answer 1

Pd between two points is energy converted from electrical potential to another form per coulomb

Question 2

What equation links energy transferred to charge and pd?

Answer 2

AE = VQ
V=W/Q
W=VIt

Question 3

What is the definition for electrical resistance?

Answer 3

Resistance of a conductor is the pd across it divided by resulting current through it R=V/I

Question 4

What causes electrical resistance?

Answer 4

Collisions between free electrons and positive ions in metal lattice transter energy

Question 5

What does a current-voltage graph for a wire at a constant temperature tell us about the resistance?

Answer 5

Constant resistance (straight line)

Question 6

Draw a current-voltage graph for a filament lamp

Answer 6

Curve increasing at a decreasing rate

Question 7

What does a current-voltage graph for a filament lamp tell us about the resistance?

Answer 7

At low voltage resistance is constant (straight line), as voltage and temperature increase resistance increases

Question 8

What is the definition of Ohm’s law?

Answer 8

Current in a metal wire at a constant temperature is proportional to the pd across it

Question 9

What does it mean if a device is non-ohmic?

Answer 9

Temperature increases and resistance increases (not constant resistance)

Question 10

What is the definition of power?

Answer 10

Energy transferred per second P=E/t

Question 11

What are 2 equations that link Power and Current?

Answer 11

P = I V and P = 1R

Question 12

What is the resistivity equation?

Answer 12

R = pL/A

Question 13

What is the unit of resistivity?

Answer 13

ohms

Question 14

What effect does doubling the radius have on the resistance of the wire?

Answer 14

A=(pie)3.14*r so doubling radius means A x 4 so R decreases by a factor of 4

Question 15

What is the definition of superconducting transition temperature Tc?

Answer 15

Temperature at which material loses all resistance and becomes superconducting

Question 16

Give an example of a metal that exhibits superconductivity and one that doesn’t

Answer 16

Zinc/Lead/Mercury exhibit superconductivity but
Copper/Silver/Gold never do

Question 17

What is the advantage of using superconducting wires?

Answer 17

No resistance so no heat loss (less power dissipated)

Question 18

Give 2 applications/uses for superconductivity

Answer 18

Nuclear fusion reactors, Large Hadron Collider, Particle accelerators, MRI scanners, Large generators

Question 19

What is the disadvantage of using superconducting wires?

Answer 19

Difficult to sustain extremely low temperatures, materials are often brittle and hard to make into a wire