Ohm's Law Et Al

Question 1

State Ohm’s Law?

Answer 1

Ohm’s Law states that provided the physical conditions of a conductor remain constant (like temperature, length of wire) the current flowing through it is directly proportional to the potential difference across it.

Question 2

Relate Resistance to Resistivity.

Answer 2

R = ρL/A
Where ρ = resistivity (in Ωm)
L = length of the wire
A = cross section area of the wire

Question 3

What is conductivity?

Answer 3

Conductivity is the inverse of Resistivity. That is,

Conductivity (σ) = 1/ρ

Question 4

What is the expression for current density?

Answer 4

Current density J is given as:

J = Eσ
Where E = electric field intensity l
σ = conductivity

Question 5

What are Ohmic materials?

Answer 5

Ohmic materials are materials which obey Ohm’s law. A good example is Copper.

Question 6

What are non-Ohmic substances?

Answer 6

These are substances which do not obey Ohm’s law. Examples include transistors, transformers, diodes, rectifiers, and semiconductors.

Question 7

What does the resistance of a wire depend on?

Answer 7

• Length of the wire
• Cross-section area of wire
• The temperature of the wire
• The nature of the wire

Question 8

What is internal resistance?

Answer 8

Internal resistance is the amount of resistance found in the electrolyte of a battery.

Question 9

What is electromotive force?

Answer 9

Electromotive force of a battery is the potential difference across the terminals of a cell when it isn’t delivering current.

Question 10

What is the expression relating the internal resistance of a cell and its EMF?

Answer 10

E = i(R + r)