1 Dual Nature Of Radiation And Matter
A monochromatic light of frequency $$v = \frac{1}{6.63} \times 10^{16}$$ Hz is produced by a laser. The power emitted is $$P = 10^{-2}$$ W. The average number of photos per second emitted by the source is
1) $$\frac{1}{(6.63)^2} \times 10^{16}$$ 2) $$(6.63)^2 \times 10^{16}$$ 3) $$10^{20}$$ 4) $$10^{16}$$
2 Work Power Energy
A mass M is attached to a massless spring of spring constant K. The mass is moved through a distance x and released. The maximum velocity of the mass is:
1) 2πM / K 2) 3) √ K /M 4) √ K / Mx
SOLUTION:−
Initial total energy of the system = KE + PE initially KE is zero and PE is (k*x2)/2 as we know, maximum velocity will be attained when the block is at the equilibrium position because at equilibrium net force on the block will be zero. now, when the block passes through the equilibrium position we have, PE is zero as there is neither expansion nor contraction in the spring KE=(m*v2)/2 applying conservation of energy gives us (m*v2)/2=(k*x2)/2
3 Atoms
What percentage of original radioactive atoms is left after five half lives?
1) 5 % 2) 3 % 3) 10 % 4) 20 %
SOLUTION
4 Gravitation
Two bodies of masses m and 4m are placed at a distance r. The gravitational potential at a point on the line joining them where the gravitational field is zero, is
5 Waves
A certain sound has an intensity 1,000,000 times greater than the faintest sound you can hear. Its intensity level is:
1) 6 dB
2) 60 dB
3) 600 dB
4) 1,000,000 dB
6 Wave Optics
Two identical lights sources S1 and S2 emit the light of same wavelength λ. These light rays will exhibit interference if
1) their phase difference remain constant 2) their phase difference is distributed randomly 3) their light intensities remain constant. 4) their light intensities change continuously
For interference to take place the light sources need to be either in phase or have a constant phase difference. In case the phase difference keeps changing the interference pattern will keep on changing, as a result of interference pattern will be observed.
7 Electric Charges And Fields
A charge q is placed at the mid-point of the line joining two equal charges each of Q. If the whole system is in equilibrium, then the value of q is
SOLUTION Potential energy of the system is equal to zero when the system is in equilibrium.
8 Work Power Energy
Consider an elliptically shaped rail PQ in the vertical plane with OP = 3 m and OQ = 4 m. A block of mass 1 kg is pulled along the rail from P to Q with a force of 18 N, which is always parallel to line PQ (see the figure given). Assuming no frictional losses, the kinetic energy of the block when it reaches Q is (n × 10) Joules. The value of n is (take acceleration due to gravity = 10 ms−2)
1) 5 2) 2 3) 3 4) 6
Work done by external force against gravity w = 18 × 5 = -90 joules, Potential energy at height U = −1 × 10 × 4 = −40 joules W =ΔU+ ΔK ΔK = W -ΔU ΔK = 90 − 40 = 50J ∴ n × 10 = 50J ∴ n = 5
9 Current Electricity
A standard cell is balanced at 150 cm. height of a potentiometer wire. If this cell is shunted by a resistance of 2 Ω, the balanced position is obtained at 100 cm. length. The internal resistance of the cell will be :
(1) 2 Ω
(2) 1 Ω
(3) 0.66 Ω
(4) 0.1Ω
The internal resistance of cell is given by :-
(l1?: balance length without shunt
10
The speed of sound in air is 343 m/s. What is the wavelength of a sound wave with a frequency of 686 Hz?
1) 4 m
2) 2 m
3) 1 m
4) 0.5 m
v =ëf, soë= v/f = (343 m/s)/(686 Hz)
= 0.5 m.
Your Score:
