HSC Science (Electronics) १२ वीं कक्षा - Maharashtra State Board Important Questions

Reactance of a coil is 157 Ω. On connecting the coil across a source of frequency 100 Hz, the current lags behind e.m.f. by 45°. The inductance of the coil is ...........

(a) 0·25 H

(b) 0·5 H

(c) 4 H

(d) 314H

A metal rod `1/sqrtpi `m long rotates about one of its ends perpendicular to a plane whose magnetic induction is 4 x 10^-3 T. Calculate the number of revolutions made by the rod per second if the e.m.f. induced between the ends of the rod is 16 mV.

If A.C. voltage is applied to a pure capacitor, then voltage across the capacitor _____________.

The magnetic flux through a loop is varying according to a relation `phi = 6t^2 + 7t + 1` where `phi` is in milliweber and t is in second. What is the e.m.f. induced in the loop at t = 2 second?

Explain self induction and mutual induction

Three capacitors of capacities 8 μF, 8 μF and 4 μF are connected in a series and potential difference of 120 volt is maintained across the combination. Calculate the charge  on capacitor of capacity 4 μF.

Derive an expression for e.m.f. and current in terms of turns ratio

In series LCR circuit at resonance, phase difference between current and e.m.f. of source is ______.

(A) `pi` rad

(B) `pi/2` rad

(C) `pi/4` rad

(D) zero rad

Prove theoretically  (electromagnetic induction) `e = (dphi)/(dt)`

Obtain an expression for the induced e.m.f. in a coil rotating with uniform angular velocity in
uniform magnetic field. Plot a graph of variation of induced e.m.f. against phase (Θ = ωt) over one cycle.

If ‘R’ is the radius of dees and ‘B’ be the magnetic field of induction in which positive charges (q) of mass (m) escape from the cyclotron, then its maximum speed (vmax) is _______.

A) `(qR)/(Bm)`

B)`(qm)/(Br)`

C) `(qBR)/m`

D) `m/(qBR)`

The width of depletion region of p-n junction diode is _______.

(A) 0.5 nm to 1 nm

(B) 5 nm to 10 nm

(C) 50 nm to 500 nm

(D) 500 nm to 1000 nm

A transformer converts 240 V AC to 60 V AC. The secondary has 75 turns. The number of turns in primary are _______.

(A) 600

(B) 500

(C) 400

(D) 300

State its any ‘two’ uses of photodiode.

Define coefficient of mutual induction. 

Explain the phenomenon of mutual induction.

Write the SI unit and dimention of of co-efficient of self induction

A capacitor of capacitance 0.5 μF is connected to a source of alternating e.m.f. of frequency 100 Hz. What is the capacitive reactance? (Π = 3.142)

At which position of the plane of the rotating coil with the direction of magnetic field, the e.m.f. induced in the coil is maximum?

Answer the following:

State the principles of the electric motor and electric generator.