#neet
- In Young's double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes : Answer: 3. four times Fringe width β=λ D/d . With d→ d/2 and D→2D : β'=λ(2D)/d/2=4β The fringe width becomes four times. Answer: option 3. 1
- The capacitance of a parallel plate capacitor with air as medium is 6 μF. With the introduction of a dielectric medium, the capacitance becomes 30 μF. The permittivity of the medium is :(ε_0 = 8.85×10^-12 C^2 N^-1 m^-2) Answer: 3. 0.44×10⁻¹⁰ C ² N ⁻¹ m ⁻² Capacitance with a dielectric of relative permittivity K is C=KC₀ . So K=30/6=5 Permittivity of the medi... 1
- Assume that light of wavelength 600 nm is coming from a star. The limit of resolution of telescope whose objective has a diameter of 2 m is : Answer: 1. 3.66×10⁻⁷ rad Limit of resolution of a telescope: Δθ=1.22λ/D . Δθ=frac1.22×600×10⁻⁹2=3.66×10⁻⁷\ rad Answer: option 1. 1
- A series LCR circuit is connected to an ac voltage source. When L is removed from the circuit, the phase difference between current and voltage is π/3. If instead C is removed from the circuit, the phase difference is again π/3 between current and vo… Answer: 3. 1.0 With L removed, the circuit is RC: tanφ=X_C/R . With C removed, it is RL: tanφ=X_L/R . Both phase angles are π/3 , so X_C=X_L... 1
- A short electric dipole has a dipole moment of 16×10^-9 C m. The electric potential due to the dipole at a point at a distance of 0.6 m from the centre of the dipole, situated on a line making an angle of 60^° with the dipole axis is :≤ft(1/4πε_0 = 9… Answer: 2. 200 V Potential of a short dipole: V=1/4πε₀pcosθ/r² . V=frac9×10⁹×16×10⁻⁹×cos60^°(0.6)²=144×0.5/0.36=200\ V Answer: option 2. 1
- An iron rod of susceptibility 599 is subjected to a magnetising field of 1200 A m^-1. The permeability of the material of the rod is :(μ_0 = 4π×10^-7 T m A^-1) Answer: 1. 2.4π×10⁻⁴ T m A ⁻¹ Relative permeability μ_r=1+chi=1+599=600 . μ=μ₀μ_r=4π×10⁻⁷×600=2.4π×10⁻⁴\ T m A⁻¹ The magnetising field 1200... 1
- A long solenoid of 50 cm length having 100 turns carries a current of 2.5 A. The magnetic field at the centre of the solenoid is :(μ_0 = 4π×10^-7 T m A^-1) Answer: 1. 6.28×10⁻⁴ T Field inside a long solenoid: B=μ₀nI , with n turns per metre. n=100/0.5=200\ m⁻¹ B=4π×10⁻⁷×200×2.5=6.28×10⁻⁴\ T Answ... 1
- A charged particle having drift velocity of 7.5×10^-4 m s^-1 in an electric field of 3×10^-10 V m^-1, has a mobility in m^2 V^-1 s^-1 of : Answer: 2. 2.5×10⁶ Mobility is drift velocity per unit electric field: μ=v_d/E . μ=frac7.5×10⁻⁴3×10⁻¹⁰=2.5×10⁶\ m²V⁻¹s⁻¹ Answer: option 2. 1
- The quantities of heat required to raise the temperature of two solid copper spheres of radii r_1 and r_2 (r_1 = 1.5 r_2) through 1 K are in the ratio : Answer: 1. 27/8 Heat needed for a 1 K rise is Q=mcΔ T . Both spheres are copper, so c is the same and Q∝ m∝ r³ . Q₁/Q₂=(r₁/r₂)³=(1.5)³=27/8... 1
- An electron is accelerated from rest through a potential difference of V volt. If the de Broglie wavelength of the electron is 1.227×10^-2 nm, the potential difference is : Answer: 4. 10⁴ V de Broglie wavelength of an electron accelerated through V volts: λ=1.227/sqrt V nm. Given λ=1.227×10⁻² nm: sqrt V=frac1.22... 1
- Taking into account of the significant figures, what is the value of 9.99 m - 0.0099 m ? Answer: 2. 9.98 m For subtraction, the result keeps as many decimal places as the number with the fewest decimal places. 9.99 has 2 decimals... 1
- A ball is thrown vertically downward with a velocity of 20 m/s from the top of a tower. It hits the ground after some time with a velocity of 80 m/s. The height of the tower is : (g = 10 m/s^2) Answer: 4. 300 m Use v²=u²+2gh (downward motion, g positive). h=v²-u²/2g=80²-20²/2×10=6400-400/20=300\ m Answer: option 4. 1
- A capillary tube of radius r is immersed in water and water rises in it to a height h. The mass of the water in the capillary is 5 g. Another capillary tube of radius 2r is immersed in water. The mass of water that will rise in this tube is : Answer: 3. 10.0 g Capillary rise: h=2Tcosθ/rρ g , so h∝1/r . Mass of water in the tube m=ρπ r²h∝ r²·1/r=r . Radius doubled gives mass double... 1
- A resistance wire connected in the left gap of a metre bridge balances a 10 Ω resistance in the right gap at a point which divides the bridge wire in the ratio 3 : 2. If the length of the resistance wire is 1.5 m, then the length of 1 Ω of the resist… Answer: 2. 1.0×10⁻¹ m Metre bridge balance: X/10=l/100-l=3/2 . X=15\ Ω This 15 Ω is the resistance of the whole 1.5 m wire. Length per ohm:... 1
- For the logic circuit shown, the truth table is :(figure: A and B each pass through a NOT gate; both outputs feed a NOR-type gate (OR gate with output bubble) giving Y) Answer: 1. A B Y: 00->0, 01->0, 10->0, 11->1 From the figure, each input goes through a NOT gate, and the outputs feed a NOR gate (OR with a... 1
- The energy equivalent of 0.5 g of a substance is : Answer: 2. 4.5×10¹³ J Use Einstein's mass-energy relation E=mc² . E=0.5×10⁻³×(3×10⁸)²=4.5×10¹³\ J Answer: option 2. Remember to convert gram... 1
- Match the following :Oxide | Nature(a) CO (i) Basic(b) BaO (ii) Neutral(c) Al_2O_3 (iii) Acidic(d) Cl_2O_7 (iv) AmphotericWhich of the following is correct option ? Answer: 2. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii) CO: neutral oxide (a)-(ii). BaO: basic oxide of an s-block metal (b)-(i). Al₂O₃ : amphoter... 1
- The rate constant for a first order reaction is 4.606×10^-3 s^-1. The time required to reduce 2.0 g of the reactant to 0.2 g is : Answer: 3. 500 s For a first-order reaction t=2.303/klog[A]₀/[A] . t=frac2.3034.606×10⁻³log2.0/0.2=frac2.3034.606×10⁻³×1=500\ s Answer: opti... 1
- An alkene on ozonolysis gives methanal as one of the product. Its structure is : Answer: 3. Cyclohexyl-CH ₂ -CH=CH ₂ Ozonolysis cleaves C=C and gives a carbonyl on each carbon. Methanal (HCHO) comes only from a terminal =... 1
- Which of the following alkane cannot be made in good yield by Wurtz reaction ? Answer: 3. n-Heptane The Wurtz reaction ( 2RX+2Na→ R-R ) gives good yield only when both alkyl groups are the same, so one alkyl halide is u... 1
- Anisole on cleavage with HI gives : Answer: 1. Phenol (C ₆ H ₅ OH) + CH ₃ I Aryl alkyl ethers are cleaved by HI at the alkyl-oxygen bond. The ether oxygen is protonated, then I... 1
- For which one of the following, Bohr model is not valid ? Answer: 4. Singly ionised neon atom (Ne ^+ ) The Bohr model works only for one-electron (hydrogen-like) systems, where the electron feels ju... 1
- The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is : (c = speed of electromagnetic waves) Answer: 2. 1 : 1 In an electromagnetic wave the energy is shared equally between the electric and magnetic fields. Electric energy density =... 1
- The Brewsters angle i_b for an interface should be : Answer: 3. 45^° < i_b < 90^° Brewster's law: tan i_b=μ , where μ is the relative refractive index of the interface. Since μ>1 for an ordinar... 1