Short Answer TypeDescribe briefly with the help of a circuit diagram, how the flow of current carries in a p-n-p transistor is regulated with emitter-base junction forward biased and base-collector junction reverse biased.
The emitter-base junction is given a small forward bias, while base collector junction is given a large reverse bias.
Under the forward biasing of emitter-base region, the positive holes of P - region move towards the base. Due to thin base most of holes (about 98%) entering it pass onto collector while a very few of them (nearly 2%) combine with the electrons of base.
As soon as a hole combines with the electron, a fresh electron leaves the negative terminal of battery VEE and enters the base. This causes a very small base current I B. The holes entering the collector move under the aiding reverse bias towards terminal C. As a hole reaches terminal C, an electron leaves the negative terminal of battery VCC and neutralizes the hole.
This causes the collector current IC . Both these currents IB and IC combine to form the emitter current Ie.
i. e., IE = IB + IC
Obviously the holes are the charge carriers within the p-n-p transistor while the electrons are charge carriers in external circuit.
In the given block diagram of a receiver, identify the boxes labelled as X and Y and write their functions.
You are given three lenses L1, L2 and L3 each of focal length 20 cm. An object is kept at 40 cm in front of L1, as shown. The final real image is formed at the focus ‘I’ of L3. Find the separations between L1, L2 and L3.
Define the terms (i) ‘cut-off voltage’ and (ii) ‘threshold frequency’ in relation to the phenomenon of photoelectric effect.
Using Einstein’s photoelectric equation shows how the cut-off voltage and threshold frequency for a given photosensitive material can be determined with the help of a suitable plot/graph.Mention three ‘different modes of propagation used in communication system. Explain with the help of a diagram how long distance communication can be achieved by ionospheric reflection of radio waves.
Draw a plot of potential energy of a pair of nucleons as a function of their separations. Mark the regions where the nuclear force is (i) attractive and (ii) repulsive. Write any two characteristic features of nuclear forces.
In a Geiger–Marsden experiment, calculate the distance of closest approach to the nucleus of Z =80, when an a-particle of 8 MeV energy impinges on it before it comes momentarily to rest and reverses its direction.
How will the distance of closest approach be affected when the kinetic energy of the a-particle is doubled?
The ground state energy of hydrogen atom is – 13.6 eV. If an electron makes a transition from an energy level – 0.85 eV to –3.4 eV, calculate the wavelength of the spectral line emitted. To which series of hydrogen spectrum does this wavelength belong?
Long Answer Type(a)
Write the expression for the force 
, acting on a charged particle of charge ‘q’, moving with a velocity in the presence of both electric field E and magnetic field B. Obtain the condition under which the particle moves un deflected through the fields.
(b)
A rectangular loop of size l × b carrying a steady current I is placed in a uniform magnetic field. Prove that the torque 
acting on the loop is given by 
is the magnetic moment of the loop.
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