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Which of the following statements is false?

1) Wheatstone bridge is the most sensitive when all the four resistances are of the same order of magnitude. 2) In a balanced Wheatstone bridge... View Article

In amplitude modulation, sinusoidal carrier frequency used is denoted by ω_c and the signal frequency is denoted by ω_m. The bandwidth (∆ω_m) of the signal is such that ∆ω_m<< ω_c. Which of the following frequencies is not contained in the modulated wave?

1) ωm 2) ωc 3) ωm + ωc 4) ωc − ωm Answer: (1) Modulated wave has a frequency range. ωc ± ωm Since, ωc >> ωm Hence, ωm is... View Article

In a common emitter amplifier circuit using an n-p-n transistor, the phase difference between the input and the output voltages will be:

1) 45o 2) 90o 3) 135o 4) 180o Answer: (4) In common emitter configuration for the n-p-n transistor, the phase difference between output... View Article

A radioactive nucleus A with a half life T, decays into a nucleus B. At t = 0, there is no nucleus B. At some time t, the ratio of the number of B to that of A is 0.3. Then, t is given by:

1) t = (T / 2) (log 2 / log 1.3) 2) t = (T) (log 1.3 / log 2) 3) t = T log (1.3) 4) t = T / [log (1.3)] Answer: (2) [No - Noe-λt] /... View Article

Some energy levels of a molecule are shown in the figure. The ratio of the wavelengths r = λ₁ / λ₂, is given by:

1) r = 4/3 2) r = 2/3 3) r = 3/4 4) r = 1/3 Answer: (4) From energy level diagram λ1 = hc/E λ2 = hc/(E/3) λ1 / λ2 = 1/ 3... View Article

A particle A of mass m and initial velocity v collides with a particle B of mass m / 2 which is at rest. The collision is head on, and elastic. The ratio of the de-Broglie wavelengths λ_A to λ_B after the collision is:

1) λA / λB = 1/3 2) λA / λB = 2 3) λA / λB = 2/3 4) λA / λB = 1/2 Answer: (2) v1 = [(m1 - m2)v / (m1 + m2)] + 0 = v / 3 p1 = m [v / 3]... View Article

In Young’s double-slit experiment, slits are separated by 0.5 mm, and the screen is placed 150 cm away. A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes on the screen. The least distance from the common central maximum to the point where the bright fringes due to both the wavelengths coincide is:

1) 1.56 mm 2) 7.8 mm 3) 9.75 mm 4) 15.6 mm Answer: (2) For λ1, y = mλ1D / d For λ2, y = nλ2D / d m / n = λ2 / λ1 = 4 / 5 For λ1, y =... View Article

A diverging lens with a magnitude of focal length 25 cm is placed at a distance of 15 cm from a converging lens of the magnitude of focal length 20 cm. A beam of parallel light falls on the diverging lens. The final image formed is:

1) real and at a distance of 40 cm from the convergent lens. 2) virtual and at a distance of 40 cm from the convergent lens. 3) real and at a... View Article

An electron beam is accelerated by a potential difference V to hit a metallic target to produce X-rays. It produces continuous as well as characteristic X-rays. If λ_min is the smallest possible wavelength of X-ray in the spectrum, the variation of log λ_min with log V is correctly represented in:

Answer: (1) In X-ray tube λmin = hc / eV In λmin = ln (hc / e) - ln V Slope is negative Intercept on the y-axis is positive.... View Article

In a coil of resistance 100 Ω, a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude of change in flux through the coil is:

1) 200 Wb 2) 225 Wb 3) 250 Wb 4) 275 Wb Answer: (3) ϵ = dɸ / dt iR = dɸ / dt ∫dɸ = R ∫i dt Magnitude of change in flux = R × area... View Article

When a current of 5 mA is passed through a galvanometer having a coil of resistance 15 Ω, it shows full-scale deflection. The value of the resistance to be put in series with the galvanometer to convert it into a voltmeter of range 0 − 10 V is:

1) 1.985 × 103 Ω 2) 2.045 × 103 Ω 3) 2.535 × 103 Ω 4) 4.005 × 103 Ω Answer: (1) ig = 5 × 10–3 A G = 15 Ω Let series resistance be R. V... View Article

A magnetic needle of magnetic moment 6.7 × 10⁻² Am² and moment of inertia 7.5 × 10⁻⁶ kg m² is performing simple harmonic oscillations in a magnetic field of 0.01 T. Time taken for 10 complete oscillations is:

1) 6.65 s 2) 8.89 s 3) 6.98 s 4) 8.76 s Answer: (1) T = 2π √I / MB = = [2π / 10] * 1.06 For 10 oscillations, t = 10T = 2π ×... View Article

In the the below given circuit diagram the current in each resistance is:

1) 1 A 2) 0.25 A 3) 0.5 A 4) 0 A Answer: (4) The potential difference in each loop is zero. ∴ No current will flow.... View Article

In the given circuit diagram when the current reaches steady state in the circuit, the charge on the capacitor of capacitance C will be:

1) CE 2) CE (r1 / r2 + r) 3) CE (r2 / r + r2) 4) CE (r1 / r1 + r) Answer: (3) In steady-state, the flow of current through the... View Article

A capacitance of 2 µF is required in an electrical circuit across a potential difference of 1.0 kV. A large number of 1 µF capacitors are available which can withstand a potential difference of not more than 300 V. The minimum number of capacitors required to achieve this is:

1) 2 2) 16 3) 24 4) 32 Answer: (4) The following arrangement will do the needful: 8 capacitors of 1µF in parallel with four such branches... View Article

An electric dipole has a fixed dipole moment p, which makes angle θ with respect to the x-axis. When subjected to an electric field E₁= E_i, it experiences a torque T₁= τ k. When subjected to another electric field E₂ = √3 E₁j it experiences a torque T₂ = – T₁. The angle θ is:

1) 30o 2) 45o 3) 60o 4) 90o Answer: (3) p = p cos θ i + p sin θ j E1 = Ei T1 = p x E1 = (p cos θ i + p sin θ j) x E (i) τ k = pE... View Article

An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave measured by the observer? (speed of light = 3 × 10⁸ ms⁻¹)

1) 10.1 GHz 2) 12.1 GHz 3) 17.3 GHz 4) 15.3 GHz Answer: (3) For relativistic motion f = fo √(c + v) / (c - v) [v = relative speed of... View Article

A particle is executing simple harmonic motion with a time period T. At time t = 0, it is at its position of equilibrium. The kinetic energy-time graph of the particle will look like:

Answer: (4) KE = (1 / 2) mω2A2cos2 ωt... View Article

The temperature of an open room of volume 30 m³ increases from 17^oC to 27^oC due to the sunshine. The atmospheric pressure in the room remains 1 × 10⁵ Pa. If n_i and n_fare the number of molecules in the room before and after heating, then n_f− n_i will be:

1) −1.61 × 1023 2) 1.38 × 1023 3) 2.5 × 1025 4) −2.5 × 1025 Answer: (4) n1 = initial number of moles n1 = P1V1 / RT1 = (105 * 30) / (8.3... View Article

C_p and C_v are specific heats at constant pressure and constant volume respectively. It is observed that

Cp − Cv = a for hydrogen gas Cp − Cv = b for nitrogen gas The correct relation between a and b is : 1) a = 1 / 14 b 2) a = b 3) a = 14 b 4)... View Article