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An axle or truck is 2.5 m long. If the truck is moving due North at ms−1 at a place where the vertical component of the earth’s magnetic field is 90 μT, the potential difference between the two ends of the axle is

a) 6.75 mV with North end positive b) 6.75 mV with West end positive c) 6.75 mV with South end... View Article

A conducting rod of length 2l is rotating with constant angular speed ω about its perpendicular bisector. A uniform magnetic field vec{B} exists parallel to the axis of rotation. The e.m.f., induced between two ends of the rod is

a) Zero b) \(\begin{array}{l}\frac{1}{2}Bwl^{2}\end{array} \) c) \(\begin{array}{l}Bwl^{2}\end{array} \) d) \(\begin{array}{l}\frac{1}{8}Bwl^{2}\end{array} \) Solution: a) Zero

A choke coil is needed to operate an arc lamp at 160V (rms) and 50Hz. The arc lamp has an effective resistance of 5Ω when running at 10A (rms). Calculate the inductance of the choke coil. If the same arc lamp is to be operated on 160V DC, what additional resistance would be required. Compare the power losses in both the cases.

Solution: \(\begin{array}{l}I_{rms}\frac{V_{rms}}{\sqrt{R^{2}+\omega^{2} L^{2}}} 25+(100πL)^{2}=16^{2} 25+10^{5}L^{2}=256\end{array} \) \(\begin{array}{l}L=\sqrt{\frac{231}{10^{5}} =0.05H\end{array} \) Let R_{A} be the additional resistance required for operating the arc... View Article

An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true?

a) The electron will continue to move with uniform velocity along the axis of the solenoid. b) The electron will... View Article

The peak value of AC is 2sqrt{2} ampere. It’s apparent value will be? – Physics Q&A

a) 0 b) 1 Ampere c) 2 Ampere d) 3 Ampere <strong>Solution:</strong>c) 2 Ampere Explanation: Apparent value is given by... View Article

The force required to stretch a spring varies with the distance as shown in the figure. If the experiment is performed with the above spring of half the length, the line OA will:-

a) Shift towards F−axis b) Shift towards X−axis c) Remains as it is d) Become double in length Solution: a)... View Article

The mobility of electrons in a semiconductor is defined as the ratio of their drift velocity to the applied electric field. If, for an n-type semiconductor, the density of electrons is 10^{19} m^{-3} and their mobility is 1.6 m^{2}/V.s then the resistivity of the semiconductor (since it is an n-type semiconductor contribution of holes is ignored) is close to:

Solution: \(\begin{array}{l}j=\sigma E=neV_{d}\end{array} \) \(\begin{array}{l}\sigma= ne\frac{V_{d}}{E}\end{array} \) = \(\begin{array}{l}ne\mu \frac{1}{\sigma}\end{array} \) = \(\begin{array}{l}\rho = \frac{1}{n_{e}e\mu_{e}}\end{array} \) \(\begin{array}{l}\frac{1}{10^{19}*1.6*10^{-19}*1.6} =0.4\Omega m\end{array} \)

Two identical cylindrical vessels, with their bases at the same level, each contain a liquid of density ρ. The height of liquid in one vessel in h1 and that in the other is h2. The area of either base is A. What is the work done by gravity in equalising the levels when the vessels are interconnected?

Solution: Refer the figure and assume that the height is h h=\(\begin{array}{l}\frac{h_{1}+h_{2}}{2}\end{array} \) \(\begin{array}{l}\Delta h=h_{1}-(\frac{h_{1}+h_{2}}{2}) = (\frac{h_{1}-h_{2}}{2})\end{array} \) Mass of... View Article

Specific rotation of the sugar solution is 0.01 SI units. 200 kgm−3 of impure sugar solution is taken in a polarimeter tube of length 0.25 m and an optical rotation of 0.4 rad is observed. The percentage of purity of sugar is the sample is

Solution: 2. 80% Explanation: Specific rotation \(\begin{array}{l}(\alpha)=\frac{\Theta}{lc}=2\end{array} \) \(\begin{array}{l}c=\frac{\Theta }{\alpha l}\end{array} \) \(\begin{array}{l}c=\frac{0.4}{0.01*0.25}=160 kg/m^{3}\end{array} \) Now percentage purity of sugar... View Article

If n, e, τ, m, are representing electron density charge, relaxation time and mass of an electron respectively then the resistance of wire of length l and cross sectional area A is given by

a) ml/ne2rA b) 2mA/ne2r c) ne2rA d) ne2rA/2m Answer:a) ml/ne2rA Solution: Relaxation time, τ = m/ne2ρ ⇒ ρ = m/ne2 τ R = ρl/A = ml/ne2 τA

The motion of a particle is defined by the equations x= 4t² and y= 2t³ in metre, where t is in seconds. Determine the normal and tangential components of the particle’s velocity and acceleration when t = 2 s.

Solution: Here, r = (4t2)i + (2t3)j v = dr/dt = (8t)i + (6t2)j when t = 2 s, v... View Article

A swimmer can swim in still water at 1.5 ms^–1. The river is flowing with 2 ms^–1 from left to right. The minimum time taken by swimmer to cross the river and the drift in that case are respectively

a) (20/9) minute, (800/3) m b) (10/9) minute, (400/3) m c) (40/9) minute, (200/3) m d) (5/3) minute, 200 m Answer: a) (20/9)... View Article

How many images will be formed if two mirrors are placed at an angle of 40⁰?

Answer: 8 Solution: The number of images formed is (360/n) – 1 here, n is the angle between the mirrors... View Article

A small ball of mass m is released from rest from a height h above the liquid surface. The density of the ball is ρ/3. Then which one of the following is incorrect? (Assume no splash)

a) If h ≥H, then the ball will be able to enter the liquid of higher density b) If h≥... View Article

The capacitor, whose capacitance is 6 μf, 3 μf and 2 μf respectively are connected with the 12-volt battery as shown in the figure. The charges on 6 μf capacitor will be

Answer: 24 x 10-6 C Solution: Combined capacity of C1 and C2 in series C’ = C1C2/(C1 + C2) = (6... View Article

Refer to the figure. The speed of the particle when its velocity becomes parallel to the inclined plane is

a) 5 m/s b) 5(√3 + 1)/2√3 m/s c) 5√3 m/s d) 5(√3 – 1) m/s Answer: d) 5(√3 – 1)... View Article

A monoatomic gas is taken in a vessel fitted with a light movable piston. If 50 cal of heat is supplied to 2 moles of gas then its rise in temperature will be (R = 2cal/mol-K)

a) 50 K b) 5 k c) 10 K d) 20 K Answer: b) 5 k Solution: Q = n Cp... View Article

A cyclist comes to a skidding stop in 10 m. During this process, the force on the cycle due to the road is 300 N and is directly opposed to the motion. How much work does the road do on the cycle?

Answer: -3000 J Solution: Force on the cycle due to road = 300 N Cyclist comes to a skidding stop in... View Article

Two vectors [latex]vec{F_{1}}[/latex] and [latex]vec{F_{2}}[/latex] each of magnitude are inclined to each other such that their resultant is to √3F then the resultant of [latex]vec{F_{1}}[/latex] and
[latex]-vec{F_{2}}[/latex] is

a) F b) √2F c) √3F d) 2F Answer: a) F Solution: Given that \(\begin{array}{l}\left|\vec{F_{1}} \right| =\left|\vec{F_{2}} \right| = \left|\vec{F} \right|\end{array} \) As we... View Article

When two spheres of equal masses undergo glancing elastic collision with one of them at rest, after the collision they will move

a) opposite to one another b) in the same direction c) together d) at right angle to each other Answer: d)... View Article

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