NEET UG
- For a plane electromagnetic wave propagating in x-direction, which one of the following combination gives the correct possible directions for electric field (E) and magnetic field (B) respectively ? Answer: 2. -j+k,\ -j-k Key idea: vec E , vec B and the direction of propagation are mutually perpendicular, and vec E×vec B points along pro... 1
- Consider the following statements (A) and (B) and identify the correct answer.(A) A zener diode is connected in reverse bias, when used as a voltage regulator.(B) The potential barrier of p-n junction lies between 0.1 V to 0.3 V. Answer: 3. (A) is correct and (B) is incorrect. Key idea: a Zener diode regulates voltage only in reverse-bias breakdown, and the barrier po... 1
- The equivalent capacitance of the combination shown in the figure is : Answer: 2. 2C Key idea: wires joining the two sides short-circuit a capacitor, and the rest become parallel. The right-hand vertical wire jo... 1
- A dipole is placed in an electric field as shown. In which direction will it move ? Answer: 2. towards the right as its potential energy will decrease. Key idea: in a non-uniform field a dipole feels a net force towards the... 1
- A parallel plate capacitor has a uniform electric field 'E' in the space between the plates. If the distance between the plates is 'd' and the area of each plate is 'A', the energy stored in the capacitor is : (ε_0 = permittivity of free space) Answer: 3. 1/2ε₀E²Ad Key idea: energy density in an electric field is 1/2ε₀E² ; multiply by the volume between the plates. U=1/2ε₀E²× Ad . O... 1
- Match Column - I and Column - II and choose the correct match from the given choices.Column - I: (A) Root mean square speed of gas molecules; (B) Pressure exerted by ideal gas; (C) Average kinetic energy of a molecule; (D) Total internal energy of 1… Answer: 3. (A) - (Q), (B) - (P), (C) - (S), (D) - (R) (A) rms speed =√(3RT/M) matches Q. (B) Pressure =1/3 nmbar v² matches P. (C) Average k... 1
- An infinitely long straight conductor carries a current of 5 A as shown. An electron is moving with a speed of 10^5 m/s parallel to the conductor. The perpendicular distance between the electron and the conductor is 20 cm at an instant. Calculate the… Answer: 4. 8×10⁻²⁰ N Key idea: the electron moves parallel to the wire, so vec v⊥vec B and F=evB . B=μ₀I/2π r=dfrac2×10⁻⁷×50.2=5×10⁻⁶\ mathr... 1
- A convex lens 'A' of focal length 20 cm and a concave lens 'B' of focal length 5 cm are kept along the same axis with a distance 'd' between them. If a parallel beam of light falling on 'A' leaves 'B' as a parallel beam, then the distance 'd' in cm w… Answer: 2. 15 Key idea: a parallel beam stays parallel only if the lens separation makes the focal points coincide. The convex lens A focuse... 1
- A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since : Answer: 4. all of the above. Key idea: for a telescope objective, large focal length gives larger magnification, and large aperture helps th... 1
- A body is executing simple harmonic motion with frequency 'n', the frequency of its potential energy is : Answer: 2. 2n Key idea: potential energy depends on x² , so it repeats twice per oscillation. x = Asinω t ⇒ U=1/2 kx²=1/2 kA²sin²ω t=1/4 kA²... 1
- Find the value of the angle of emergence from the prism. Refractive index of the glass is √(3). Answer: 1. 60^° Key idea: a ray hitting a face along its normal goes straight in; then apply Snell's law at the next face. The ray enters th... 1
- A spring is stretched by 5 cm by a force 10 N. The time period of the oscillations when a mass of 2 kg is suspended by it is : Answer: 4. 0.628 s Key idea: find k from the stretch, then use T=2π√(m/k) . k=F/x=10/0.05=200\ N/m T=2π√(2/200)=2π×0.1=0.628\ mathrm s . Opt... 1
- If force [F], acceleration [A] and time [T] are chosen as the fundamental physical quantities. Find the dimensions of energy. Answer: 2. [F][A][ T² ] Key idea: write energy as work = force × distance, and express the distance through acceleration and time. L = 1/2 A... 1
- A cup of coffee cools from 90°C to 80°C in t minutes, when the room temperature is 20°C. The time taken by a similar cup of coffee to cool from 80°C to 60°C at a room temperature same at 20°C is : Answer: 2. 13/5t Key idea: Newton's law of cooling in the average-temperature form: Δ T/t=k(T_avg-T₀) . First case: 10/t=k(85-20)=65k⇒ k=2/1... 1
- The velocity of a small ball of mass M and density d, when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is d/2, then the viscous force acting on the ball will be : Answer: 1. Mg/2 Key idea: at constant (terminal) velocity the net force is zero: weight = buoyancy + viscous force. Volume of ball V=M/d . B... 1
- A particle is released from height S from the surface of the Earth. At a certain height its kinetic energy is three times its potential energy. The height from the surface of earth and the speed of the particle at that instant are respectively : Answer: 4. S/4, √(3gS/2) Key idea: total mechanical energy mgS is conserved (taking the surface as zero of potential energy). At height h: U... 1
- When a uranium isotope ^235_92U is bombarded with a neutron, it generates ^89_36Kr, three neutrons and : Answer: 1. ¹⁴⁴₅₆ Ba Balance mass number and atomic number. Left: ²³⁵₉₂U+¹₀n gives A=236,\ Z=92 . Right: ⁸⁹₃₆Kr+3 ¹₀n+^A_Z X . A=236-89-3=144... 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 color code of a resistance is given below :(figure: colour bands Yellow, Violet, Brown, Gold)The values of resistance and tolerance, respectively, are : Answer: 4. 470 Ω , 5% Four-band colour code: first two bands are digits, the third is the multiplier, the fourth is tolerance. Yellow = 4, V... 1
- Which of the following graph represents the variation of resistivity (ρ) with temperature (T) for copper ? Answer: 3. graph (3) For a metal like copper, resistivity rises with temperature because lattice vibrations scatter electrons more: ρ=ρ₀[1+α... 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
- 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
- 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
- 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