MEC | Physics
An n-type semiconductor is obtained by doping pure silicon with
Answer: phosphorus
Model set 1, Q46: explanation →A full-wave rectifier is fed with a 50 Hz AC supply. The frequency of the output ripple is
Answer: 100 Hz
Model set 1, Q47: explanation →Which of the following is a universal logic gate?
Answer: NAND
Model set 1, Q48: explanation →A transistor has current gain $\beta = 50$ and base current $40\ \mu$A. The collector current is
Answer: 2 mA
Model set 1, Q49: explanation →Resistors of $6\ \Omega$ and $3\ \Omega$ are connected in parallel. The equivalent resistance is
Answer: $2\ \Omega$
Model set 1, Q26: explanation →A heater of power 2 kW is connected to a 250 V supply. The current drawn is
Answer: 8 A
Model set 1, Q27: explanation →One kilowatt-hour is equal to
Answer: $3.6\times10^6$ J
Model set 1, Q28: explanation →A gas absorbs 500 J of heat and does 200 J of work on the surroundings. The change in its internal energy is
Answer: 300 J
Model set 1, Q14: explanation →In an isothermal process of an ideal gas, the
Answer: internal energy does not change
Model set 1, Q16: explanation →The magnetic flux through a coil falls from 0.5 Wb to 0.1 Wb in 0.2 s. The magnitude of the induced emf is
Answer: 2 V
Model set 1, Q31: explanation →A transformer has 100 turns in the primary and 500 turns in the secondary. For 20 V applied to the primary, the secondary voltage is
Answer: 100 V
Model set 1, Q32: explanation →Capacitors of $6\ \mu$F and $3\ \mu$F are connected in series. The equivalent capacitance is
Answer: $2\ \mu$F
Model set 1, Q37: explanation →The energy stored in a $10\ \mu$F capacitor charged to 100 V is
Answer: 0.05 J
Model set 1, Q38: explanation →Light of photon energy 3 eV falls on a metal of work function 2 eV. The maximum kinetic energy of photoelectrons is
Answer: 1 eV
Model set 1, Q39: explanation →The energy of a photon of wavelength 620 nm is about
Answer: 2 eV
Model set 1, Q40: explanation →If the momentum of a particle is doubled, its de Broglie wavelength
Answer: becomes half
Model set 1, Q41: explanation →The energy of the electron in the $n = 2$ orbit of a hydrogen atom is
Answer: -3.4 eV
Model set 1, Q42: explanation →The half-life of a radioactive sample is 10 days. The fraction left after 30 days is
Answer: 1/8
Model set 1, Q43: explanation →A nuclear reaction has a mass defect of 0.02 u. The energy released is (1 u = 931.5 MeV)
Answer: 18.63 MeV
Model set 1, Q50: explanation →A car starts from rest and accelerates uniformly at $2\ \mathrm{m/s^2}$ for $10\ \mathrm{s}$. The distance covered is
Answer: 100 m
Model set 1, Q1: explanation →The dimensional formula of pressure is
Answer: $ML^{-1}T^{-2}$
Model set 1, Q2: explanation →Two forces of 3 N and 4 N act at right angles on a body. The magnitude of their resultant is
Answer: 5 N
Model set 1, Q3: explanation →A 5 kg block is pulled along a rough floor by a 30 N horizontal force. The friction force is 10 N. The acceleration of the block is
Answer: $4\ \mathrm{m/s^2}$
Model set 1, Q4: explanation →A 2 kg ball is lifted through 5 m at constant speed. Work done against gravity is ($g = 10\ \mathrm{m/s^2}$)
Answer: 100 J
Model set 1, Q5: explanation →The acceleration due to gravity at a point at distance $2R$ from the centre of the Earth (R = radius) is
Answer: $g/4$
Model set 1, Q6: explanation →A 0.5 kg mass moves in a circle of radius 2 m with a speed of 4 m/s. The centripetal force is
Answer: 4 N
Model set 1, Q7: explanation →A wire of cross-section $1\ \mathrm{mm^2}$ carries a stretching force of 100 N and the strain produced is $10^{-3}$. Young's modulus of the wire is
Answer: $10^{11}\ \mathrm{N/m^2}$
Model set 1, Q8: explanation →A disc of moment of inertia $2\ \mathrm{kg,m^2}$ rotates at $10\ \mathrm{rad/s}$. Its rotational kinetic energy is
Answer: 100 J
Model set 1, Q9: explanation →If the length of a simple pendulum is made four times, its time period
Answer: becomes double
Model set 1, Q10: explanation →Heat required to raise the temperature of 2 kg of water by $10^\circ$C is ($c = 4200\ \mathrm{J/kg,K}$)
Answer: 84000 J
Model set 1, Q11: explanation →The temperature at which Celsius and Fahrenheit scales give the same reading is
Answer: $-40^\circ$
Model set 1, Q12: explanation →A metal rod 2 m long ($\alpha = 1.2\times10^{-5}\ \mathrm{K^{-1}}$) is heated by $50\ \mathrm{K}$. Its increase in length is
Answer: 1.2 mm
Model set 1, Q13: explanation →A Carnot engine works between 400 K and 300 K. Its efficiency is
Answer: 25%
Model set 1, Q15: explanation →For conduction through a slab, if the thickness is doubled with the same area and temperature difference, the rate of heat flow
Answer: becomes half
Model set 1, Q17: explanation →A wave has frequency 50 Hz and wavelength 4 m. Its speed is
Answer: $200\ \mathrm{m/s}$
Model set 1, Q18: explanation →The fundamental frequency of a closed organ pipe 0.5 m long is (speed of sound = 340 m/s)
Answer: 170 Hz
Model set 1, Q19: explanation →Two tuning forks of frequencies 256 Hz and 260 Hz are sounded together. The number of beats heard per second is
Answer: 4
Model set 1, Q20: explanation →An object is placed 30 cm in front of a concave mirror of focal length 10 cm. The image forms at a distance of
Answer: 15 cm
Model set 1, Q21: explanation →The refractive index of glass is 1.5. The speed of light in glass is ($c = 3\times10^8\ \mathrm{m/s}$)
Answer: $2\times10^8\ \mathrm{m/s}$
Model set 1, Q22: explanation →The power of a converging lens of focal length 25 cm is
Answer: +4 D
Model set 1, Q23: explanation →In Young's double slit experiment, $\lambda = 600$ nm, $D = 1$ m and $d = 0.6$ mm. The fringe width is
Answer: 1 mm
Model set 1, Q24: explanation →Light is completely polarised on reflection from a surface of refractive index $\sqrt{3}$. The angle of incidence is
Answer: $60^\circ$
Model set 1, Q25: explanation →A cell of emf 12 V and internal resistance $1\ \Omega$ is connected to an external resistance of $5\ \Omega$. The terminal potential difference is
Answer: 10 V
Model set 1, Q29: explanation →A 0.5 m wire carrying 4 A is placed perpendicular to a magnetic field of 0.5 T. The force on the wire is
Answer: 1 N
Model set 1, Q30: explanation →An AC source has a peak voltage of 100 V. Its rms voltage is about
Answer: 70.7 V
Model set 1, Q33: explanation →A material that is weakly repelled by a magnet is called
Answer: diamagnetic
Model set 1, Q34: explanation →Two charges of $2\ \mu$C and $3\ \mu$C are 0.3 m apart in air. The force between them is
Answer: 0.6 N
Model set 1, Q35: explanation →If the distance from a point charge is doubled, the electric field strength becomes
Answer: one quarter
Model set 1, Q36: explanation →The number of neutrons in a nucleus of $^{238}_{92}\mathrm{U}$ is
Answer: 146
Model set 1, Q44: explanation →The minimum wavelength of X-rays produced at an accelerating voltage of 40 kV is about
Answer: $0.31\ \text{\AA}$
Model set 1, Q45: explanation →