Current of Electricity

Question 1

Define electric current

Answer 1

An electric current is the rate of flow of charge.

Question 2

Formula for transport of charges

Answer 2

Q=Nq. Where N is number of charged particles and q is charge of particles

Question 3

Define coulomb

Answer 3

1 coulomb is the quantity of charge that flows through a point in 1 second, given 1 ampere of constant current. Q=IT

Question 4

Formula for finding I in terms of A and v

Answer 4

I=nAqv

Question 5

Define drift velocity

Answer 5

Drift velocity is the average velocity of ALL the free electrons and is not a measure of the actual velocity of any particular electron.

Question 6

Formula of Potential Difference

Answer 6

V = Va-Vb = W/Q

Question 7

Definition of Potential Difference

Answer 7

The potential difference, V, between 2 points of a circuit is the electrical energy converted per unit charge into other forms of energy when charges move between the 2 points.

Question 8

Definition of Resistance of a conductor

Answer 8

A conductor’s resistance, R, is defined as the ratio of potential difference, V, across it to the current, I, flowing in it.

Question 9

Formula for Power

Answer 9

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

Question 10

State Ohm’s Law

Answer 10

Ohm’s Law states that for a conductor at a constant temperature, the current in the conductor is directly proportional to the potential difference across it.

Question 11

Define resistivity

Answer 11

The resistivity, p, of a material, is numerically equal to the resistance between opposite faces of a cube of material, of unit length and unit cross-sectional area. p = RA/L

Question 12

Define Electromotive Force

Answer 12

The electromotive force of a source is the amount of energy converted from other forms into electrical energy per unit charge driven through the source round a complete circuit.

Question 13

Circuit equation formula (for internal resistance questions)

Answer 13

Potential rise = potential drop
E = Ir + IR (known as circuit equation)
I = E/(R + r)

Question 14

When circuit is open (internal resistance)

Answer 14

V = E

Question 15

When circuit is closed (internal resistance)

Answer 15

V = E - Ir

Question 16

When does a battery deliver maximum power? (internal resistance)

Answer 16

When load resistance is equal to internal resistance.

Question 17

Formula for efficiency (n)

Answer 17

n = R/(R + r)

Question 18

Define Ampere

Answer 18

Ampere is defined as unit of electric current equal to the flow of 1 coulomb per second through a point in a circuit.

Question 19

Define Volt

Answer 19

Colt is defined as potential difference between 2points in an electrical circuit when 1 joule of electrical energy is converted to other forms of energy as 1 coulomb of charge passes from one point to the other.

Question 20

Define Ohm

Answer 20

Ohm is defined as resistance between 2 points in an electrical circuit when a constant p.d. of 1 volt produces 1 ampere of current.

Question 21

Define internal resistance

Answer 21

Internal resistance is the resistance a charge encounters when moving through a material source.

Question 21

Define Power

Answer 21

Power of a device is the rate at which resistance converts electrical energy to other forms of energy.

Question 22

Describe electrical conduction in a metal

Answer 22

In metal free electrons are charge carriers.
Conduction is due to flow of free electrons through crystal lattice of positive cations.
Electric field setup by externally connected battery which establishes a force on electrons to travel toward +ve terminal with a drift velocity.
In external electric field (inside battery/ material), the free electrons accelerate and drift towards higher potential.
KE and momentum of electrons increases but encounter cations in path, resulting in deflection, and jerky and slower motion.

Question 23

State and explain the factors that affect terminal voltage of a battery

Answer 23

Current and internal resistance of battery. When no current passes through internal resistor, terminal voltage is given by e.m.f of battery. When current passes through terminal voltage is given by V= E - Ir.