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a parallel plate capacitor of capacitance 90 pf is connected to a battery of emf 20v if a dielectric material of dielectric constant k equal 5 by 3 is inserted between the plates the magnitude of the induced charge will be

a. 2.4 nC b. 0.9 nC c. 1.2 nC d. 0.3 nC Solution: Option (c) 1.2 nC Explanation: Battery remains connected as dielectric is introduced So... View Article

An electron, a proton and an alpha particle having the same kinetic energy are moving in circular orbits of radii r_e, r_p, r_α respectively in a uniform magnetic field B. The relation between r_e, r_p, r_α is:

a. re < rp < rα b. re < rα < rp c. re > rp = rα d. re < rp = rα Answer: (d) r = mv/qB = p/qB K... View Article

The reading of the ammeter for a silicon diode in the given circuit is:

a. 11.5 mA b. 13.5 mA c. 0 d. 15 mA Answer: (a) Knowledge based Si diode has forward bias resistance 200 at 2 V 400 at 1 V ⇒ here Rfb <... View Article

An electron from various excited states of hydrogen atom emit radiation to come to the ground state. Let λ_n, λ_g be the de Broglie wavelength of the electron in the n^th state and the ground state respectively. Let A_n be the wavelength of the emitted photon in the transition from the n^th state to the ground state. For large n, (A, B are constants)

a. Λ2n≈ A+B λ2n b. Λ2n≈ λ c. Λn≈A + (B/ λ2n) d. Λn≈A + Bλn Answer: (c) mvr = (nh/2 π) λde Broglie = (h/p) = (2 πr/n) λn =(2 πrn/n)... View Article

Unpolarized light of intensity I passes through an ideal polarizer A. Another identical polarizer B is placed behind A. the intensity of light beyond B is found to be I/2. Now another identical polarizer C is placed between A and B. The intensity beyond B is now found to be I/8. The angle between polarizer A and C is:

a. 450 b. 600 c. 00 d. 300 Answer: (a) Unpolarized light passes the A I after A = I/2 I after B = I/2 (given) The angle between A and B is 900... View Article

If the series limit frequency of the Lyman series is v_L, then the series limit frequency of the Pfund series is:

a. vL/16 b. vL/25 c. 25vL d. 16vL Answer: (b) Series limit is Lyman : ∞ → 1 P fund :∞ → 5 vLyman = RC vPfund... View Article

Two masses m₁ = 5 kg and m₂ = 10 kg, connected by an inextensible string over a frictionless pulley, are moving as shown in the figure. The coefficient of friction of horizontal surface is 0.15. The minimum weight m that should be put on top of m2 to stop the motion is:

a. 43.3 Kg b. 10.3 Kg c. 18.3 Kg d. 27.3 Kg Answer: (d) At equilibrium fr = T = m1g frmax =(m2 + m)g (10+m)g =5g 10 +m = 5/0.15... View Article

A particle is moving in a circular path of radius a under the action of an attractive potential U = -k/2r². Its total energy is

a. zero b. c. d. Answer: (a) F= -k/r3 Centripetal force Total Energy E = K + U = 0... View Article

Two batteries with e.m.f. 12 V and 13 V are connected in parallel across a load resistor of 10 Ω. The internal resistances of the two batteries are 1 Ω and 2 Ω respectively. The voltage across the load lies between.

a. 11.4 V and 11.5 V b. 11.7 V and 11.8 V c. 11.6 V and 11.7 V d. 11.5 V and 11.6 V Answer: (d)... View Article

A solid sphere of radius r made of a soft material of bulk modulus K is surrounded by a liquid in a cylindrical container. A mass less piston of area a floats on the surface of the liquid, covering entire cross section of cylindrical container. When a mass m is placed on the surface of the piston to compress the liquid, the fractional decrement in the radius of the sphere,(dr/r) is:

a. mg/3Ka b. mg/Ka c. Ka/mg d. Ka/3mg Answer: (a) Bulk modulus -------(1) ---------(2) From eq.(1) and (2)... View Article

The mass of a hydrogen molecule is 3.32 x 10^-27 kg. If 10²³ hydrogen molecules strike, per second, a fixed wall of area 2 cm² at an angle of 45⁰ to the normal, and rebound elastically with a speed of 10³ m/s, then the pressure on the wall is nearly:

a. 2.35 x 102 N/m2 b. 4.70 x 102 N/m2 c. 2.35 x 103 N/m2 d. 4.70 x 103 N/m2 Answer: (a) Change in momentum of one molecule Force... View Article

It is found that if a neutron suffers an elastic collinear collision with deuterium at rest, fractional oss of its energy is p_d; while for its similar collision with carbon nucleus at rest, fractional loss of energy is p_C. The values of p_d and p_c are respectively:

a. (0, 0) b. (0, 1) c. (.89,.28) d. (.28,.89) Answer: (c) L.M.C mV1 + 2m V2 = mV0 V1 + 2V2 = V0 …(1) V2 – V1 = V0…(2) On solving V2 = 2V0/3... View Article

A liquid of coefficient of viscosity [latex]eta =1[/latex]poise is flowing in a pipe of radius 3 cm on such that the rate of volume flow is 1000 / min. determine the Reynolds numbers.

a. 3536 b. 3500 c. 3400 d. 3600 Answer: (a) = 1 poise r = 3 cm = 3536... View Article

A block of mass 4 kg is suspended from the ceiling with the help of a steel wire off radius 2 mm and negligible mass. Find the stress in the wire (g = π²)

a. 4 × 106 b. 3 × 105 c. 3.14 × 106 d. 2 × 106 Answer: (c) = 3.14 × 106 N/m2... View Article

Find out the no of reflection after which light ray will exit from (Given sin 40° = 0.64)

a. 130000 b. 57803 c. 140000 d. 150000 Answer: (b) For one reflection ∴ = 57803... View Article

Force displacement graph of a particle starting from rest is given in the figure shown. The kinetic energy of particle at x = 3m is

a. 6.5 J b. 7.5 J c. 6 J d. 5 J Answer: (a) Area under graph is work done = 6.5J... View Article

An A.C source of voltage V = 220 sin (100 πt) volts is connected with R = 50 Ω. The time interval in which the current goes from its peak value to half of the peak value is

a. b. c. d. Answer: (c) For oscillation to go from max to half is T / 6... View Article

A conducting slider of resistance R (10 Ω) mass 50 g & length 10 cm is kept on a U – shaped frame as shown in figure. There is uniform magnetic field (B = 0.1T) perpendicular to plane of frame. These slider is attached to a spring (K = 0.5 N/m). It is displaced by A_Ɵ& released time is which amplitude become A /e is

a. 9000 s b. 10000 s c. 12000 s d. 15000 s Answer: b Comparing with & A = A0e(-b/2m)t... View Article

A converging lens of focal length 20 cm is placed between an object & a concave mirror of focal mirror of focal length 10 cm as shown in figure. The final image is

a. Coinciding with object, enlarged, Inverted real b. Coinciding with object, same size, erect, real c. Coinciding with object, same size,... View Article

Four particle each of mass m are undergoing circular motion under the influence of action of their mutual gravitational interaction while being at the vertices of a square of side a. Their speeds are

a. b. c. d. Answer: (b) Gravitation Force = mv2/r r =... View Article