Section B
10) Write ampere's circuital theatem. Using the same theorem find the magnetic field at a distancer
away from a long straight current carrying wire.
11) Derive the expression for drift velocity of free electron in terms of relaxation time and electric field
applied across a conductor
12) Capacitor blocks DC. Why?
Section C
13) (a) What is meant by resonance in LCR Circuit?
(b) Obtain the resonant frequency and Q-factor of a series LCR circuit with L = 3H, C = 27F, R=
14) Three charges q..q2 and q, are kept respectively at points A, B and C as shown in figures. Writet
expression for electrostatic potential energy of the system.
15) How can you convert a moving coil galvanometer into ammeter and voltmeter?
mach case Take the resis
Answers
Answer:
10) Let MN be a long straight wire carrying current and P a point at distance
′
a
′
from wire where magnetic field B has to be found
using Ampere's circuital law, let us consider a circle element dl at P
⇒∮B.dl=μ
0
I
B is constant everywhere on the loop
⇒B∮dl=μ
0
I
⇒B×2πa=μ
0
I
⇒B=(
4π
μ
0
)×
a
2I
11)Here m = mass of election, e = charge, E = electric field. The average time difference between two consecutive collisions is known as relaxation time of election. ... Hence, relaxation time decreases with increase in temperature which implies that drift velocity also decreases with temperature.
12) We know that there is no frequency i.e. 0Hz frequency in DC supply. If we put frequency “f = 0″ in the inductive reactance (which is AC resistance in capacitive circuit) formula. If we put XC as infinity, the value of current would be zero. That is the exact reason why a capacitor block DC.
13) (a) The resonance of a series RLC circuit occurs when the inductive and capacitive reactances are equal in magnitude but cancel each other because they are 180 degrees apart in phase. The sharp minimum in impedance which occurs is useful in tuning applications.
( b) Resonant angular frequency ωo = 1 / ( L C )1/2 = 1/ ( 3 × 27 × 10-6 )1/2 = 1000/9 ≈ 111 rad/s.
Resonant frequency is obtained from , ωo = 2×π×fo ; fo = 111/ (2π) = 17.7 Hz.
Q-factor , Q = ωo L / R = 111 × 3 / 7.4 = 333/7.4 = 45.
14) above
15) galvanometer has a resistance G and current ia flowing in it, produces full scale deflection. If S1 is the value of shunt which converts it into an ammeter of range 0−i and S2 is the value of the shunt for the range 0−2i.
