#neet
- The resistance of platinum wire at 0^°C is 2 Ω and 6.8 Ω at 80^°C. The temperature coefficient of resistance of the wire is : Answer: 4. 3×10⁻² ^°C⁻¹ R_t=R₀(1+α t) , so α=R_t-R₀/R₀ t . α=6.8-2/2×80=4.8/160=3×10⁻² ^°C⁻¹ . The answer is 3×10⁻² ^°C⁻¹ . 1
- The net impedance of circuit (as shown in figure) will be : Answer: 4. 5√(5) Ω For a series LCR circuit Z=√(R²+(X_L-X_C)²) . X_L=2π fL=2π(50)50/π×10⁻³=5 Ω . X_C=1/2π fC=dfrac12π(50)10³/π×10⁻⁶=10 Ω . Z... 1
- For the following logic circuit, the truth table is: Answer: 3. A B Y: 0 0 0; 0 1 1; 1 0 1; 1 1 1 The inputs A and B pass through NOT gates, and the results go into a NAND gate. Y=bar A·bar B=A... 1
- 10 resistors, each of resistance R are connected in series to a battery of emf E and negligible internal resistance. Then those are connected in parallel to the same battery, the current is increased n times. The value of n is : Answer: 3. 100 Series: R_s=10R , so I₁=E/10R . Parallel: R_p=R/10 , so I₂=10E/R . n=I₂/I₁=10E/R/E/10R=100 . The answer is 100. 1
- Calculate the maximum acceleration of a moving car so that a body lying on the floor of the car remains stationary. The coefficient of static friction between the body and the floor is 0.15 (g=10 m s^-2). Answer: 4. 1.5 mathrmm s⁻² The body stays at rest relative to the car only while the pseudo-force ma is balanced by static friction, whose m... 1
- The x-t graph of a particle performing simple harmonic motion is shown in the figure. The acceleration of the particle at t=2 s is : Answer: 1. -π²/16 mathrmm s⁻² From the graph, the amplitude is A=1 m and the particle is at the maximum at t=2 s, with a zero crossing at 4... 1
- A satellite is orbiting just above the surface of the earth with period T. If d is the density of the earth and G is the universal constant of gravitation, the quantity 3π/Gd represents : Answer: 3. T² For a satellite just above the surface, r=R and T=2π√(R³/GM) , so T²=4π²R³/GM . With M=4/3π R³d : T²=4π²R³/G·4/3π R³d=3π/Gd .... 1
- The net magnetic flux through any closed surface is : Answer: 2. Zero Magnetic monopoles do not exist, so field lines always form closed loops: every line entering a closed surface also leaves i... 1
- The work functions of Caesium (Cs), Potassium (K) and Sodium (Na) are 2.14 eV, 2.30 eV and 2.75 eV respectively. If incident electromagnetic radiation has an incident energy of 2.20 eV, which of these photosensitive surfaces may emit photoelectrons? Answer: 2. Cs only A surface emits photoelectrons only if the photon energy is at least its work function. Cs: 2.20 ≥ 2.14 eV, so it emits.... 1
- If the galvanometer G does not show any deflection in the circuit shown, the value of R is given by : Answer: 4. 100 Ω No deflection means no current in the galvanometer branch, so the potential drop across R equals the 2 V cell. Current in t... 1
- A 12 V, 60 W lamp is connected to the secondary of a step down transformer, whose primary is connected to ac mains of 220 V. Assuming the transformer to be ideal, what is the current in the primary winding? Answer: 2. 0.27 A An ideal transformer has no loss, so input power equals output power. Output power = 60 W, so V_pI_p = 60⇒ I_p=60/220≈ 0.2... 1
- A full wave rectifier circuit consists of two p-n junction diodes, a centre-tapped transformer, capacitor and a load resistance. Which of these components remove the ac ripple from the rectified output? Answer: 4. Capacitor The rectifier output is pulsating dc. A capacitor connected across the load charges at the peaks and discharges in the... 1
- In a plane electromagnetic wave travelling in free space, the electric field component oscillates sinusoidally at a frequency of 2.0×10^10 Hz and amplitude 48 V m^-1. Then the amplitude of oscillating magnetic field is : (Speed of light in free space… Answer: 4. 1.6×10⁻⁷ T In an electromagnetic wave in free space, E₀ = cB₀ . B₀=E₀/c=dfrac483×10⁸=1.6×10⁻⁷ T. The frequency is not needed. The... 1
- A metal wire has mass (0.4±0.002) g, radius (0.3±0.001) mm and length (5±0.02) cm. The maximum possible percentage error in the measurement of density will nearly be: Answer: 4. 1.6% Density ρ=m/π r² l . The maximum fractional errors add, with the radius error counted twice because of r² . Δρ/ρ=Δ m/m+2Δ r/... 1
- Light travels a distance x in time t_1 in air and 10x in time t_2 in another denser medium. What is the critical angle for this medium? Answer: 1. sin⁻¹(10t₁/t₂) Refractive index n=c/v , and the critical angle satisfies sin C=1/n=v/c . Speed in air: c=x/t₁ . Speed in the medi... 1
- An electric dipole is placed at an angle of 30^° with an electric field of intensity 2×10^5 N C^-1. It experiences a torque equal to 4 N m. Calculate the magnitude of charge on the dipole, if the dipole length is 2 cm. Answer: 1. 2 mC Torque on a dipole: τ = pEsinθ , with p=q· l . 4 = q(0.02)(2×10⁵)sin30^° = q× 2000 q = 2×10⁻³ C = 2 mC. 1
- Let a wire be suspended from the ceiling (rigid support) and stretched by a weight W attached at its free end. The longitudinal stress at any point of cross-sectional area A of the wire is : Answer: 3. W/A The wire is in equilibrium under the weight W at the free end (the wire's own weight is neglected). The tension at every cros... 1
- In hydrogen spectrum, the shortest wavelength in the Balmer series is λ. The shortest wavelength in the Bracket series is : Answer: 3. 4λ The shortest wavelength of a series comes from the transition from n=∞ to the series' lower level n₁ : dfrac1λ=R/n₁² , so λ∝ n... 1
- The temperature of a gas is -50^° C. To what temperature the gas should be heated so that the rms speed is increased by 3 times? Answer: 3. 3295^° C v_rms∝√(T) . The key reads \"increased by 3 times\" as the speed becoming v+3v=4v . T₁ = -50+273=223 K. v₂/v₁=4⇒ T₂=16T₁... 1
- A football player is moving southward and suddenly turns eastward with the same speed to avoid an opponent. The force that acts on the player while turning is : Answer: 4. along north-east Force is along the change in velocity, vec F∝ Δvec v=vec v_f-vec v_i . Initially the velocity is southward, -vha... 1
- The ratio of frequencies of fundamental harmonic produced by an open pipe to that of closed pipe having the same length is : Answer: 3. 2 : 1 Fundamental frequency of an open pipe: f_o=v/2L . For a closed pipe: f_c=v/4L . f_o/f_c=4L/2L=2:1 . The answer is 2 : 1. 1
- The angular acceleration of a body, moving along the circumference of a circle, is : Answer: 1. along the axis of rotation Angular acceleration vecα = dvecω/dt is a vector along the axis of rotation, like vecω . For rotation... 1
- Given below are two statements:Statement I : Photovoltaic devices can convert optical radiation into electricity.Statement II : Zener diode is designed to operate under reverse bias in breakdown region.In the light of the above statements, choose the… Answer: 2. Both Statement I and Statement II are correct. Statement I is correct: photovoltaic devices (solar cells) convert optical radiati... 1
- If _S E· dS=0 over a surface, then : Answer: 2. the number of flux lines entering the surface must be equal to the number of flux lines leaving it. oint vec E· dvec S = q_enc/ε₀... 1