AS Physics Unit 1.10 Resistance And Resisitivity

Question 1

What is the definition of Ohm’s Law?

Answer 1

Ohm’s Law states that the current through a metallic conductor is directly proportional to the applied potential difference, providing the temperature is constant.

Question 2

What is the equation and units for resistance?

Answer 2

R = V / I
This is where R = resistance in ohms, V = potential difference in volts, I = current in amperes.

Question 3

What are the two equations that link the power and resistance equations?

Answer 3

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

Question 4

What is the current like in a series circuit?

Answer 4

It is the same anywhere.

Question 5

What is the voltage like in a series circuit?

Answer 5

The voltage is shared across each of the series components.

Question 6

What is the current like in a parallel circuit?

Answer 6

It is shared across each of the parallel components.

Question 7

What is the voltage like in a parallel circuit?

Answer 7

It is the same anywhere in a parallel circuit.

Question 8

What rate the two equations to add resistors in parallel?

Answer 8

1 / RT = 1 / R1 + 1 / R2
RT = (R1 * R2) / (R1 + R2)

Question 9

What is the definition of resistivity?

Answer 9

Resistivity is defined as being the numerical value or the resistance between the two opposite faces of a 1m cube or material.

Question 10

What is the equation and units of resistivity?

Answer 10

R = P x (L / A)
P = R x (A / L)

Question 11

What are the units for resistivity?

Answer 11

Ohm meter (Nm)

Question 12

What is 1mm^2 equal to in m^2?

Answer 12

1 x 10 ^ -6 m^2

Question 13

What is the equation for the cross sectional area of a circle?

Answer 13

πd^2 / 4

Question 14

What is the definition of a superconductor?

Answer 14

We can define a material as a superconductor if it loses all its electrical resistivity to become a perfect conductor when it is below its critical temperature.

Question 15

What is the temperature that is known as absolute zero?

Answer 15

-273 degrees or 0K is absolute zero on the thermodynamic scale of temperature.

Question 16

When was superconductivity discovered and what was the metal tested?

Answer 16

It was discovered in 1911 by a Dutch physicist and his experiment was about the resistivity of mercury.

Question 17

What happens at -273 degrees or 0K?

Answer 17

All molecular motion ceases and metals have no resistance.

Question 18

Where can we find superconductors in today’s world?

Answer 18

They can be found in MRI scanners and in Maglev (magnetic levitation) transport. This eliminates friction.

Question 19

What happens as temperature rises for non-metals?

Answer 19

Resistance falls quite significantly.

Question 20

Why does this happen in non-metals?

Answer 20

Non-metals have many more electrons in their outer shell that become available for conduction after thermal release.

Question 21

What are semi-conductors at low temperatures?

Answer 21

Good insulators.

Question 22

Why are semi-conductors bad insulators at higher temperatures?

Answer 22

As temperature increases their conductivity increases. They are said to have a negative temperature coefficient (NTC) of resistance.

Question 23

What is one of the two things that can happen when the temperature of a metal is increased?

Answer 23

The outer shell or conduction electrons in the atoms can be released by thermal agitation.

Question 24

What is the other thing that can happen as the temperature of a metal is increased?

Answer 24

The atoms begin to vibrate with both a greater frequency and larger amplitude. This means that the electrons have an increased chance of collisions.