Physics
- A 10 μ F capacitor is connected to a 210 V, 50 Hz source as shown in figure. The peak current in the circuit is nearly (π=3.14): Answer: 3. 0.93 A Key idea: For a capacitor in an AC circuit the capacitive reactance is X_C=1/ω C and the peak current is I₀=V₀/X_C=V₀ω C ,... 1
- A parallel plate capacitor is charged by connecting it to a battery through a resistor. If I is the current in the circuit, then in the gap between the plates : Answer: 3. displacement current of magnitude equal to I flows in the same direction as I. Key idea: Maxwell's displacement current I_d=ε₀dΦ_... 1
- The property which is not of an electromagnetic wave travelling in free space is that : Answer: 1. they originate from charges moving with uniform speed. Key idea: Electromagnetic waves are produced by accelerated (oscillating)... 1
- If the plates of a parallel plate capacitor connected to a battery are moved close to each other, thenA. the charge stored in it, increases.B. the energy stored in it, decreases.C. its capacitance increases.D. the ratio of charge to its potential rem… Answer: 3. A, C and E only Key idea: The capacitor stays connected to the battery, so the voltage V stays fixed. Moving the plates closer re... 1
- The minimum energy required to launch a satellite of mass m from the surface of earth of mass M and radius R in a circular orbit at an altitude of 2R from the surface of the earth is: Answer: 2. 5GmM/6R Key idea: The minimum energy is the difference between the total energy in the orbit and the total energy at the surface.... 1
- The velocity (v) - time (t) plot of the motion of a body is shown below :The acceleration (a) - time (t) graph that best suits this motion is : Answer: 4. graph (4) Key idea: Acceleration is the slope of the v - t graph. Initially v=0 and flat: a=0 . Straight rise: constant positive... 1
- The following graph represents the T-V curves of an ideal gas (where T is the temperature and V the volume) at three pressures P_1, P_2 and P_3 compared with those of Charles's law represented as dotted lines.Then the correct relation is: Answer: 1. P₁>P₂>P₃ Key idea: For an ideal gas PV=nRT , so at fixed pressure T=P/nRV : the T-V line has slope P/nR . A larger pressure gives... 1
- An iron bar of length L has magnetic moment M. It is bent at the middle of its length such that the two arms make an angle 60^° with each other. The magnetic moment of this new magnet is: Answer: 3. M/2 Key idea: Magnetic moment = pole strength × distance between the poles. Bending changes this distance, not the pole strength.... 1
- A small telescope has an objective of focal length 140 cm and an eye piece of focal length 5.0 cm. The magnifying power of telescope for viewing a distant object is: Answer: 3. 28 Key idea: For a telescope in normal adjustment (distant object), m=f_o/f_e . m=140/5.0=28 . Option 3. 1
- If the mass of the bob in a simple pendulum is increased to thrice its original mass and its length is made half its original length, then the new time period of oscillation is x/2 times its original time period. Then the value of x is: Answer: 3. sqrt2 Key idea: T=2π√(L/g) does not depend on the mass of the bob. Only the length changes: T'=2π√(L/2/g)=T/sqrt2 . Setting T/sqr... 1
- A force defined by F=α t^2+β t acts on a particle at a given time t. The factor which is dimensionless, if α and β are constants, is: Answer: 3. α t/β Key idea: Every term in a physical formula has the same dimensions as F , so α t² and β t have the dimensions of force. Equ... 1
- A metallic bar of Young's modulus, 0.5×10^11 N m^-2 and coefficient of linear thermal expansion 10^-5 ^°C^-1, length 1 m and area of cross-section 10^-3 m^2 is heated from 0^°C to 100^°C without expansion or bending. The compressive force developed i… Answer: 3. 50×10³ N Key idea: If the bar is not allowed to expand, the thermal strain αΔ T is cancelled by a compressive strain, so a stress... 1
- Given below are two statements :Statement I : Atoms are electrically neutral as they contain equal number of positive and negative charges.Statement II : Atoms of each element are stable and emit their characteristic spectrum.In the light of the abov… Answer: 4. Statement I is correct but Statement II is incorrect. Key idea: Check each statement on its own. Statement I: An atom has equal n... 1
- ^290_82X α Y e^+ Z β^- P e^- QIn the nuclear emission stated above, the mass number and atomic number of the product Q respectively, are : Answer: 1. 286, 81 Key idea: α emission lowers A by 4 and Z by 2; β^+ (positron) lowers Z by 1; β^- (electron) raises Z by 1. The mass numbe... 1
- The terminal voltage of the battery, whose emf is 10 V and internal resistance 1 Ω, when connected through an external resistance of 4 Ω as shown in the figure is : Answer: 4. 8 V Key idea: Terminal voltage V=ε-Ir . Current I=ε/R+r=10/4+1=2 A. V=10-2×1=8 V (equivalently IR=2×4=8 V). Option 4. 1
- If c is the velocity of light in free space, the correct statements about photon among the following are :A. The energy of a photon is E=h.B. The velocity of a photon is c.C. The momentum of a photon, p=h/c.D. In a photon-electron collision, both tot… Answer: 3. A, B, C and D only Key idea: Go through the properties of a photon. A: E=hν . True. B: Speed is c . True. C: p=hν/c=frac hλ . Tru... 1
- In an ideal transformer, the turns ratio is N_p/N_s=1/2. The ratio V_s : V_p is equal to (the symbols carry their usual meaning) : Answer: 3. 2 : 1 Key idea: For an ideal transformer V_s/V_p=N_s/N_p . Given N_p/N_s=1/2 , we get N_s/N_p=2 , so V_s:V_p=2:1 . It is a step-u... 1
- In the above diagram, a strong bar magnet is moving towards solenoid-2 from solenoid-1. The direction of induced current in solenoid-1 and that in solenoid-2, respectively, are through the directions: Answer: 2. AB and DC Key idea: Lenz's law: the induced current opposes the change in flux, so a solenoid end facing a moving magnet behaves... 1
- A logic circuit provides the output Y as per the following truth table :| A | B | Y ||---|---|---|| 0 | 0 | 1 || 0 | 1 | 0 || 1 | 0 | 1 || 1 | 1 | 0 |The expression for the output Y is : Answer: 4. B Key idea: Read the truth table to see what Y depends on. Y is 1 when B=0 and 0 when B=1 , whatever A is (rows 1 and 3, and rows... 1
- In the following circuit, the equivalent capacitance between terminal A and terminal B is : Answer: 2. 2 μ F Key idea: The circuit is symmetric, so the middle capacitor is part of a balanced bridge and holds no charge. Let M be the... 1
- Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.Assertion A : The potential (V) at any axial point, at 2 m distance(r) from the centre of the dipole of dipole moment vector P of magnitude, 4×10^-6… Answer: 4. A is true but R is false. Key idea: Potential of a dipole at an axial point: V=±p/4πε₀r² . Assertion: V=frac9×10⁹×4×10⁻⁶2²=9×10³... 1
- A thin spherical shell is charged by some source. The potential difference between the two points C and P (in V) shown in the figure is:(Take 1/4πε_0=9×10^9 SI units) Answer: 1. zero Key idea: For a charged shell, the potential is the same at every point inside and on the surface: V=kq/R . C is the centre... 1
- The mass of a planet is 1/10th that of the earth and its diameter is half that of the earth. The acceleration due to gravity on that planet is : Answer: 1. 3.92 m s ⁻² Key idea: g=GM/R² . For the planet M_p=M/10 and R_p=R/2 , so g_p=G(M/10)/(R/2)²=4/10 g=0.4×9.8=3.92\ m s⁻² Option 1. 1
- A bob is whirled in a horizontal plane by means of a string with an initial speed of ω rpm. The tension in the string is T. If speed becomes 2ω while keeping the same radius, the tension in the string becomes : Answer: 3. 4T Key idea: The tension supplies the centripetal force: T=mω²r . With the same m and r , T∝ω² . Doubling the speed (rpm) gives T... 1