Physics
- A horizontal force 10 N is applied to a block A as shown in figure. The mass of blocks A and B are 2 kg and 3 kg, respectively. The blocks slide over a frictionless surface. The force exerted by block A on block B is : Answer: 4. 6 N Key idea: Both blocks move together with the same acceleration. Find it first, then use it for block B. a=F/m_A+m_B=10/2+3=2... 1
- A tightly wound 100 turns coil of radius 10 cm carries a current of 7 A. The magnitude of the magnetic field at the centre of the coil is (Take permeability of free space as 4π×10^-7 SI units): Answer: 4. 4.4 mT Key idea: Field at the centre of a circular coil of N turns: B=μ₀NI/2R . B=frac4π×10⁻⁷×100×72×0.1=frac8.8×10⁻⁴0.2≈4.4×10⁻³... 1
- If the monochromatic source in Young's double slit experiment is replaced by white light, then Answer: 4. there will be a central bright white fringe surrounded by a few coloured fringes. Key idea: Each colour makes its own fringe patt... 1
- If x=5≤ft(π t+π/3)m represents the motion of a particle executing simple harmonic motion, the amplitude and time period of motion, respectively, are : Answer: 3. 5 m, 2 s Key idea: Compare with the standard SHM form x=Asin(ω t+φ) . Here A=5 m and ω=π rad/s. Time period T=2π/ω=2π/π=2 s. Ampl... 1
- The quantities which have the same dimensions as those of solid angle are : Answer: 2. strain and angle Key idea: Solid angle (like plane angle) is a ratio of two lengths/areas, so it is dimensionless. Strain (change... 1
- The maximum elongation of a steel wire of 1 m length if the elastic limit of steel and its Young's modulus, respectively, are 8×10^8 N m^-2 and 2×10^11 N m^-2, is : Answer: 2. 4 mm Key idea: The largest stress the wire can bear without permanent change is the elastic limit. Use Y=stress/strain . Strain =... 1
- A thin flat circular disc of radius 4.5 cm is placed gently over the surface of water. If surface tension of water is 0.07 Nm^-1, then the excess force required to take it away from the surface is : Answer: 2. 19.8 mN Key idea: The surface-tension force acts along the line of contact between the disc and the water, which is the circumfer... 1
- A wheel of a bullock cart is rolling on a level road as shown in the figure below. If its linear speed is v in the direction shown, which one of the following options is correct (P and Q are any highest and lowest points on the wheel, respectively)? Answer: 3. Point P moves faster than point Q . Key idea: In pure rolling, each point has speed = (speed of centre) + (rotational speed about... 1
- A thermodynamic system is taken through the cycle abcda. The work done by the gas along the path bc is : Answer: 2. zero Key idea: Work done by a gas is W=∫ P dV , so it is zero when the volume does not change. In the figure, path bc is vertical... 1
- Two bodies A and B of same mass undergo completely inelastic one dimensional collision. The body A moves with velocity v_1 while body B is at rest before collision. The velocity of the system after collision is v_2. The ratio v_1 : v_2 is : Answer: 3. 2:1 Key idea: In a completely inelastic collision the bodies stick together and momentum is conserved. mv₁+0=(m+m)v₂ , so v₂=v₁/2... 1
- At any instant of time t, the displacement of any particle is given by 2t-1 (SI unit) under the influence of force of 5N. The value of instantaneous power is (in SI unit): Answer: 2. 10 Key idea: Instantaneous power P=vec F·vec v . Velocity v=d/dt(2t-1)=2 m/s (constant). Then P=Fv=5×2=10 W. Option 2. 1
- Match List I with List II.List I (Spectral Lines of Hydrogen for transitions from): A. n_2=3 to n_1=2; B. n_2=4 to n_1=2; C. n_2=5 to n_1=2; D. n_2=6 to n_1=2List II (Wavelengths (nm)): I. 410.2; II. 434.1; III. 656.3; IV. 486.1Choose the correct ans… Answer: 3. A-III, B-IV, C-II, D-I Key idea: These are Balmer lines (transitions to n=2 ); a larger jump means more energy and a shorter wave... 1
- A wire of length 'l' and resistance 100 Ω is divided into 10 equal parts. The first 5 parts are connected in series while the next 5 parts are connected in parallel. The two combinations are again connected in series. The resistance of this final com… Answer: 3. 52 Ω Key idea: Each of the 10 equal parts has resistance 100/10=10\ Ω . Five parts in series: 5×10=50\ Ω . Five parts in parallel... 1
- The graph which shows the variation of ≤ft(1/λ^2) and its kinetic energy, E is (where λ is de Broglie wavelength of a free particle) : Answer: 1. graph (1) Key idea: For a free particle E=p²/2m and λ=h/p . So E=h²/2mλ² , which gives frac1λ²=2m/h²E . frac1λ² is directly propo... 1
- Consider the following statements A and B and identify the correct answer :A. For a solar-cell, the I-V characteristics lies in the IV quadrant of the given graph.B. In a reverse biased pn junction diode, the current measured in (μ A), is due to majo… Answer: 2. A is correct but B is incorrect. Key idea: Check each statement separately. A: A solar cell works as a generator, so its I-V curv... 1
- The output (Y) of the given logic gate is similar to the output of an/a : Answer: 1. AND gate Key idea: Find the output of each first-stage gate, then apply the final NOR gate. With the inputs of each gate joined,... 1
- In a vernier calipers, (N+1) divisions of vernier scale coincide with N divisions of main scale. If 1 MSD represents 0.1 mm, the vernier constant (in cm) is : Answer: 3. 1/100(N+1) Key idea: Vernier constant = 1 MSD - 1 VSD. N main scale divisions equal N+1 vernier divisions, so 1 VSD=N/N+1 MSD . V... 1
- A particle moving with uniform speed in a circular path maintains : Answer: 1. varying velocity and varying acceleration. Key idea: Velocity and acceleration are vectors, so a change in direction counts as a... 1
- Match List-I with List-II.List-I (Material): A. Diamagnetic; B. Ferromagnetic; C. Paramagnetic; D. Non-magneticList-II (Susceptibility ()): I. =0; II. 0>≥-1; III. 1; IV. 0<<ε (a small positive number)Choose the correct answer from the options given b… Answer: 2. A-II, B-III, C-IV, D-I Key idea: The sign and size of magnetic susceptibility chi identify the type of material. Diamagnetic: chi... 1
- In a uniform magnetic field of 0.049 T, a magnetic needle performs 20 complete oscillations in 5 seconds as shown. The moment of inertia of the needle is 9.8×10^-6 kg m^2. If the magnitude of magnetic moment of the needle is x×10^-5 Am^2; then the va… Answer: 1. 1280 π² Key idea: A magnetic needle in a field oscillates like a torsional pendulum: T=2π√(I/MB) . Period T=5/20=0.25 s. Squaring... 1
- An unpolarised light beam strikes a glass surface at Brewster's angle. Then Answer: 1. the reflected light will be completely polarised but the refracted light will be partially polarised. Key idea: At Brewster's ang... 1
- A light ray enters through a right angled prism at point P with the angle of incidence 30^° as shown in figure. It travels through the prism parallel to its base BC and emerges along the face AC. The refractive index of the prism is: Answer: 3. sqrt5/2 Key idea: The ray leaves along face AC, so its angle of incidence on AC is the critical angle C , with sin C=frac1μ . Let... 1
- The moment of inertia of a thin rod about an axis passing through its mid point and perpendicular to the rod is 2400 g cm^2. The length of the 400 g rod is nearly : Answer: 2. 8.5 cm Key idea: For a thin rod about its midpoint and perpendicular to its length, I=ML²/12 . L²=12I/M=12×2400/400=72 , so L=√(7... 1
- An electric dipole is placed as shown in the figure. The electric potential (in 10^2 V) at point P due to the dipole is (ε_0 = permittivity of free space and 1/4πε_0=K): Answer: 2. (3/8)qK P lies on the axis of the dipole. Distances from P: to +q it is 5-3=2 cm, to -q it is 5+3=8 cm. V=Kq(dfrac10.02-dfrac10.0... 1