Current of Electricity

Question 1

What is charge

Answer 1

Chare is the property of a particle that cause and interaction of the particle with other charged particles and material of electrical nature

Q=Ne

Question 2

What is electric current

Answer 2

I is the rate of flow of charge

I = Q/t

Question 3

What is equation relating current and drift velocity

Answer 3

I = Q/t = nAvq

- A is cross-sectional are
- n is number of electrons per unit volume

Question 4

What is electromotive force

Answer 4

It can be defined as the energy converted into electrical energy from other forms per unit charge in driving a charge around a complete circuit

E=W/Q

- W is energy converted to electrical energy
- Q is amount of charge moving around a complete circuit

Question 5

What is potential difference

Answer 5

p.d. across a conductor or btw 2 points in a circuit is defined as the amount of electrical energy converted to other forms of energy per unit charge pass it through it or across the 2 points

V = W/Q

Question 6

What is a volt

Answer 6

1 volt is defined as the p.d. if 1 joule of electrical energy is converted to other forms of energy per coulomb of charge passing through it or across the 2 points

Question 7

What is resistance

Answer 7

Electrical resistance of a conductor is defined as the ratio of the potential difference across the conductor to the current flowing through the conductor

R=V/I

Question 8

What is an ohm

Answer 8

1 ohm is defined as the resistance of a conductor when the potential difference is one volt per ampere of current flowing through it

Question 9

What is ohm’s law

Answer 9

Ohm’s law states that the current through a metallic conductor is directly proportional to the potential difference across it, provided the temperature and other physical conditions are kept constant

Question 10

I-V characteristic of an ohmic resistor

Answer 10

It is a pure metallic conductor at constant temperature. It obeys Ohm’s law and has a constant resistance. Hence the I-V relationship is a straight line through the origin.

Question 11

I-V characteristic of filament lamp

Answer 11

When the current is small, the temperature of the filament lamp is so low the resistance of the filament remains constant. When the current is large, the temperature of the filament wire increases. The lattice ions vibrate more vigourously and the conducting electrons collide more frequently with the lattice ions, hindering the flow of electrons. Hence the resistance of the filament lamp increases with increased temperature and the line bends towards larger V to I ratio.

Question 12

I-V characteristic of negative temperature coefficient thermistor

Answer 12

A thermistor is made of semiconductor material such as carbon Silicon or germanium. An increase in voltage and the corresponding increase in current cause a rise in temperature. This would increase the thermal agitation of the atoms and set free more electrons and holes in the crystal lattice. This increase in the concentration of charge carriers decreases the resistance. The effect outweighs the increase in resistance due to the increase in frequency of collisions with the lattice ions. Overall the resistance decreases and the line bends towards a smaller V to I ratio.

Question 13

I-V characteristics of semiconductor diodes

Answer 13

A diode is a device that passes current in one direction only. When forward-biased, it conducts with negligible resistance when the p.d. exceeds a certain value. When reverse-biased, only a very small leakage current flows due to a very large resistance

Question 14

What is the resistance R of a uniform conductor of length L and cross sectional area A

Answer 14

R = ρL/A

Question 15

What is power dissipated in the resistor

Answer 15

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

Question 16

What is the current in a circuit with resistor R and internal resistance r

Answer 16

I = E/(R+r)

Question 17

What is the terminal p.d.

Answer 17

It is the p.d. across the terminals of the cell. It is less than the e.m.f. E of the cell.

Vr = IR = E - Ir

Question 18

What is the efficiency of a circuit

Answer 18

η = I^2R/I^2(R+r) = R/(R+r)

Question 19

What is the maximum power theorem

Answer 19

It states that the maximum power is delivered to the load when the resistance of the load R is equal to the internal resistance r of the source