NEET UG

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A horizontal bridge is built across a river. A student standing on the bridge throws a small ball vertically upwards with a velocity 4 m s^-1. The ball strikes the water surface after 4 s. The height of bridge above water surface is (Take g=10 m s^-2… Answer: 4. 64 m Take upward as positive. The ball starts with u=+4 m/s, and its displacement at the water is -h after 4 s. s=ut-1/2gt²⇒ -h=4... Uniformly accelerated motion relations 1 answer
A very long conducting wire is bent in a semi-circular shape from A to B as shown in figure. The magnetic field at point P for steady current configuration is given by : Answer: 4. μ₀ i/4R[1-2/π] pointed away from page Add the fields of the three parts at P: two semi-infinite straight wires and one semicircle... Biot-Savart law, field of circular loop 1 answer
A wire carrying a current I along the positive x-axis has length L. It is kept in a magnetic field B=(2i+3j-4k) T. The magnitude of the magnetic force acting on the wire is : Answer: 4. 5 IL Force on a wire: vec F=I vec L×vec B with vec L=Lhat i . hat i×(2hat i+3hat j-4hat k)=3hat k+4hat j (since hat i×hat j=hat k... Force on current-carrying conductor, force between parallel currents 1 answer
Two thin lenses are of same focal lengths (f), but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be : Answer: 1. Infinite For lenses in contact, 1/F=dfrac1f₁+dfrac1f₂ . f₁=+f , f₂=-f : 1/F=1/f-1/f=0 , so F=∞ . The combination behaves like a p... Magnification, power of lens, combination of thin lenses 1 answer
In the figure shown here, what is the equivalent focal length of the combination of lenses (Assume that all layers are thin)? Answer: 4. -100 cm Add the powers of the two refracting surfaces of the lens ( n=1.5 ) placed in a medium of index 1.6 , using P=n₂-n₁/R . S... Magnification, power of lens, combination of thin lenses 1 answer
The radius of inner most orbit of hydrogen atom is 5.3×10^-11 m. What is the radius of third allowed orbit of hydrogen atom? Answer: 1. 4.77 mathringA Bohr orbit radius: r_n=n² r₁ . Third orbit: r₃=9×5.3×10⁻¹¹=4.77×10⁻¹⁰ m = 4.77 Å (1 Å = 10⁻¹⁰ m). Bohr model, energy levels, hydrogen spectrum 1 answer
The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to ≤ft(1/16)^th of its initial value? Answer: 1. 80 minutes Activity falls by half every half-life. dfrac116=(1/2)⁴ , so 4 half-lives are needed. t=4×20=80 minutes. The answer is... Composition and size of nucleus, atomic masses 1 answer
The magnitude and direction of the current in the following circuit is Answer: 3. 0.5 A from A to B through E In the loop the two cells oppose each other (10 V and 5 V), so the net emf is 10-5=5 V. The 10 V cell... Kirchhoff's laws and applications 1 answer
Resistance of a carbon resistor determined from colour codes is (22000±5\%) Ω. The colour of third band must be : Answer: 4. Orange Colour code: first two bands give the digits, the third band gives the power of ten (multiplier), the fourth gives toleran... Ohm's law, resistance, V-I characteristics of ohmic and non-ohmic conductors 1 answer
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 . Resistivity, conductivity and temperature dependence of resistance 1 answer
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. Series and parallel combination of resistors 1 answer
The minimum wavelength of X-rays produced by an electron accelerated through a potential difference of V volts is proportional to: Answer: 3. 1/V The shortest X-ray wavelength occurs when the electron gives all its kinetic energy to one photon: eV=dfrachcλ_min . λ_min=hc... Einstein's photoelectric equation, particle nature of light 1 answer
In a series LCR circuit, the inductance L is 10 mH, capacitance C is 1 μF and resistance R is 100 Ω. The frequency at which resonance occurs is : Answer: 1. 1.59 kHz Resonance occurs when X_L=X_C : f₀=1/2π√(LC) . Resistance does not affect it. LC=10×10⁻³×10⁻⁶=10⁻⁸ , so √(LC)=10⁻⁴ s. f₀... Reactance, impedance, LCR series circuit, resonance 1 answer
An ac source is connected to a capacitor C. Due to decrease in its operating frequency : Answer: 4. displacement current decreases. Capacitive reactance X_C=1/2π fC . When the frequency decreases, X_C increases. The current (and... Reactance, impedance, LCR series circuit, resonance 1 answer
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... Reactance, impedance, LCR series circuit, resonance 1 answer
The magnetic energy stored in an inductor of inductance 4 μH carrying a current of 2 A is : Answer: 1. 8 μ J Energy stored in an inductor: U=1/2LI² . U=1/2×(4×10⁻⁶)×(2)² = 8×10⁻⁶ J = 8 μ J. Self and mutual inductance 1 answer
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... Logic gates (OR, AND, NOT, NAND, NOR) 1 answer
The equivalent capacitance of the system shown in the following circuit is : Answer: 2. 2 μ F From the figure, one 3 μ F capacitor is in series with a parallel pair of 3 μ F capacitors. Parallel pair: 3+3=6 μ F. Serie... Capacitors, series and parallel combination, parallel plate capacitor with/without dielectric 1 answer
Two bodies of mass m and 9m are placed at a distance R. The gravitational potential on the line joining the bodies where the gravitational field equals zero, will be (G = gravitational constant) : Answer: 4. -16Gm/R Find the point where the net field is zero, then add the potentials of both masses there. Let the point be at distance x... Gravitational potential energy and gravitational potential 1 answer
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 .... Motion of a satellite: orbital velocity, time period and energy 1 answer
A vehicle travels half the distance with speed v and the remaining distance with speed 2v. Its average speed is: Answer: 4. 4v/3 Average speed = total distance / total time. Let the total distance be 2s . t₁=s/v , t₂=s/2v , total time =3s/2v . v_avg=2s/... Frame of reference, motion in a straight line, speed and velocity 1 answer
A bullet is fired from a gun at the speed of 280 m s^-1 in the direction 30^° above the horizontal. The maximum height attained by the bullet is (g=9.8 m s^-2,\ 30^°=0.5) : Answer: 4. 1000 m Maximum height: H=u²sin²θ/2g . H=(280)²(0.5)²/2×9.8=78400×0.25/19.6=1000 m. The answer is 1000 m. Projectile motion 1 answer
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... Static and kinetic friction, laws of friction, rolling friction 1 answer
For Young's double slit experiment, two statements are given below:Statement I : If screen is moved away from the plane of slits, angular separation of the fringes remains constant.Statement II : If the monochromatic source is replaced by another mon… Answer: 4. Statement I is true but Statement II is false. Fringe width β=λ D/d , so angular separation θ=β/D=λ/d . Statement I: θ does not d... Interference and Young's double-slit experiment 1 answer

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