Current Electricity

Question 1

1. Electric Current

2. Ohm’s Law

Answer 1

1. Q = It
2. V = IR
   R = rho L/A

Question 2

Current density (j)
Vector form of current density-

Answer 2

j = i/a
j = sigma E

i = J.A

Question 3

Drift Velocity

Answer 3

Vd = -eE X t /m (remove t will give acceleration)

Question 4

Relation between drift velocity and current

Answer 4

I = neAVd
j= -neVd

Question 5

Mobility

Answer 5

mu = vd/ E

Question 6

Carbon Resistor

Answer 6

B 0
B 1
R 2
O 3
Y 4
G 5
B 6
V 7
G 8
W 9
GOLD 5%
SILVER 10%
NO COLOUR 20%

Question 7

Temperature dependence of resistivity

1. metal
2. semiconductor

Answer 7

1. For metals, the resistivity increases with increase in temperature.
   ΡT = ρ˳ [ 1 + α (T - T˳)]
2. For semiconductors, resistivity decreases with increase in temperature

Question 8

Combination of resistors

1. Series combination
2. Parallel combination

Answer 8

1. V = V1 + V2
   R = R1 + R2
2. I = I1 +I2
   1/R = 1/ R1 + 1/R2

Question 9

Cells in Series and Parallel

Answer 9

1. Equivalent EMF/Resistance of Cells in Series
   E1 + E2 + E3 + …….En
   r = r1 + r2+ r3 + rn
2. Equivalent EMF/Resistance of Cells in Parallel
   r = (1r1 + 1r2 + 1r3 +…….. 1rn )-1

Question 10

Kirchhoff’s laws
A) Junction law
B) Loop law

Answer 10

1. At any junction, the sum of the currents entering the junction is
   equal to the sum of the currents leaving the junction.
2. The algebraic sum of changes in potential around any closed loop involving resistors and the cells in the lop is zero.
   This is based on the law of conservation of energy.
   V-IR_1-IR_2-IR_3=0

Question 11

Wheatstone Bridge

Answer 11

R2/R1 = R4/R3

Question 12

Meter Bridge

Answer 12

X = RL2/L1 = R(100 – L)/L

Question 13

COMPARING EMF OF 2 CELLS

Answer 13

e1 / e2 = l1 / l2