Doubtly
@Doubtly · Joined Feb 2021
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- A particle of mass rotates in a circle which has a vertical boundary of radius 0.2 meter, rotating in horizontal plane. The correct option is option 1) 9.8 × 10^(–4) N N=mω²R =(0.2)[ 4π²over T²](R) =0.24(9.8)over 1600(0.2) =9.8×10⁻⁴ N 1
- A bar magnet of length 14 cm is placed along N-S direction with north of magnetic along north direction. If horizontal component The correct option is 1) 2.88 Am^(2 ) 1
- An antenna of length 25 m is mounted on top of a building of height 75 m. The correct option is 1)100 m Length of antenna ≥ λover 4 λ ≤ 4×25 λ ≤100m 1
- Three gases O2, N2 and Co2 having masses 16g, 28g and 44g respectively are filled in a container of volume V The correct option is 4) 5over 2 RTover V PV=(16over32+ 28over28+ 44over44)RT p=5over 2 RTover V 1
- Four small balls are placed at the corner of a square of length l. Evaluate MOI of system about a line passing through A and parallel to BD. The correct option is 2) 3 ml² I=2m(loversqrt2)² +m(sqrt2l)² =2ml²over 2+2ml²=3ml² 1
- In photoelectric effect stopping potential for electromagnetic radiations depends on Correct option is 4)frequency In photoelectric effect stopping potential for electromagnetic radiations depends on frequency 1
- A simple pendulum attached to ceiling of lift has time period T when lift is at rest. The correct option is 1) √(2over 3)T T=2π lover g T'=2π lover g+gover2 therefore T'over T= sqrt gover 3g over2 T'=Tsqrt 2over3 1
- Relation between energy density of electric field (UE) and magnetic field (UB) will be: correct answer is 3) U_E=U_(B ) Average energy density of electric field and magnetic field are same. 1
- A common transistor radio set requires 12V (D.C.) for its operation. The D.C. source is constructed by using a transformer The correct answer is 440 N_pover N_s=V_pover V_s N_pover24=220over12 N_p=200×24over12 N_p=440 1
- An audio signal υm = 20sin2π(1500t) amplitude modulates a carrier υc =80 sin 2π (100,000t). The value of percent modulation is ________. Correct answer is 25 v_m = 20 sin [100π t+πover4] :v_c = 80 sin [10⁴π t+πover6] we know that, modulation index = A_mover A_c from given equa... 1
- A resonance circuit having inductance and resistance 2 × 10–4 H and 6.28 Ω respectively oscillates at 10 MHz frequency. correct answer is 2000 R = 6.28 Ω f = 10 MHz L = 2 × 10⁻⁴ Henry We know that quality factor Q is given by ⇒ Q = X_L / R = ωL / R also, ω = 2... 1
- Each side of a box made of metal sheet in cubic shape is ‘a’ at room temperature ‘T’, the coefficient of linear expansion of the metal sheet is ‘α’. The correct Answer is C) 3a³αΔT ΔV = VγΔT ΔV = 3a³αΔT 2
- The work done by a gas molecule in an isolated system is given by, W = α.β2.e-x2 / αkT, where x is the displacement, k is the Boltzmann constant and T is the The correct option is c) MLT^(-2 ) we knnow that ,x² / α.k.T = dimensionless [x² / α.k.T ] = [M⁰L⁰T⁰] [α] = [L² / k.T] ⇒ [κ] = [M¹L²T⁻²K⁻¹]... 1
- The focal length f is related to the radius of curvature r of the spherical convex mirror by: The correct Answer is B) f = +½ r Explaination : So, r / 2 = f f = +½ r 1
- A current through a wire depends on time as i = α0t + βt2 where α0 = 20 A/s and β = 8 As-2. Find the charge crossed through a section of the wire in 15 s. Correct Answer is B) 11250 C Explaination :: we have , i = α₀t + βt² , α = 20 A/s and β = 8As⁻² ,t = 15 sec We know that , i= dqover dt⇒ ∫₀^... 1
- Statement-I: Two photons having equal linear momenta have equal wavelengths. Statement-II: If the wavelength of a photon is decreased, Correct option is d) Statement-I is true but Statement-II is false Energy of photon E = hc / λ = E ∝ 1 / λ Hence, energy of photon increases... 1
- Consider two satellites S1 and S2 with periods of revolution 1 hr and 8 hr respectively revolving around a planet in circular orbits. The correct answer is A) 8:1 we have formula , ω = 2over T given the, ratio of time period T₁over T₂=1over8 from formula, ω ∝ 1over T ω₁ ove... 1
- Four identical particles of equal masses 1 kg made to move along the circumference of a circle of radius 1 m under the action of their own mutual gravitational The correct option is A) space√( (1+2sqrt2)Gspace over2) explaination:: By resolving force F₂, we get F₁ + F₂ cos 45° + F₂ cos 45° = F_c F₁... 2