Resistance

Question 1

What happens if you put potential difference across an electrical component?

Answer 1

A current will flow

Question 2

What does the amount of current for a certain p.d. depend?

Answer 2

Resistance of the component.

Question 3

What is the resistance defined as?

Answer 3

• Measure of the difficulty of making current pass through the component.
• potential difference / current
R = V / I
Unit of resistance is the ohm, Ω

Question 4

What is the formula for voltage & current?

Answer 4

I = V / R

Question 5

What is a resistor?

Answer 5

• Component designed to have a certain resistance, which is the same regardless of the current through it.

Question 6

Why must the voltmeter be in parallel?

Answer 6

So no current can pass through the voltmeter, otherwise the ammeter will not record the exact current through the resistor.

Question 7

What is the purpose of a variable resistor?

Answer 7

A variable resistor is used to adjust the current and PD as necessary.

Question 8

What is the V/I graph for a resistor?

Answer 8

• Straight line through the origin, as the resistance remains the same regardless of the current.
• Gradient is constant, at any point is equal to the pd / I, which equals resistance.
• pd across the resistor is proportional to the current.

Question 9

What is ohm’s law?

Answer 9

PD across a metallic conductor is proportional tot he current through it, provided the physical conditions do not change.

Question 10

What is the gradient of a graph with current on Y and voltage on X?

Answer 10

1/resistance

Question 11

What are conductors that obey ohm’s law called?

Answer 11

Ohmic conductors

Question 12

What is the formula for resistance of a conductor of length L, cross sectional area, A?

Answer 12

Resistance, R is proportional to L, inversely proportional to A.
R = p x L / A
p = resistivity

Question 13

What is the method to determining the resistivity of a wire?

Answer 13

• Measure diameter of a wire, using a micrometer at several different points along the wire, calculate mean diameter, use to calculate cross sectional area.
• Measure resistance, R at different lengths, L of wire.
• Plot graph of R against L
• Gradient x Cross sectional = Resistivity

Question 14

What is a superconductor?

Answer 14

Wire/Device made of material that has zero resistivity at and below a critical temperature, that depends on the material.