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For a plane convex lens (μ=1.5) having radius of curvature 10cm. It is silvered on its plane surface. Find focal length after silvering (1) 10cm (2) 20cm (3) 15cm (4) 25cm

Answer: (1) 10cm An optical lens is generally made up of two spherical surfaces. If those surfaces are bent outwards, the lens is called a... View Article

Calculate the ratio of 4th Bohr’s to 2nd Bohr’s orbit of He⁺ ion.

Answer: The Bohr model suggests that the electrons in atoms are in various energy orbits around the nucleus. In defining these orbits of varying... View Article

A ball initially at rest and it is dropped from building of height 10 m to ground. If the coefficient of restitution is e = 0.7. After collision, the ball rebounds back up to height h, find the value of h. (g = 9.8 m/s²)

Answer: A ball initially at rest and it is dropped from building of height 10 m to ground. If the coefficient of restitution is e = 0.7. After... View Article

A body starts from rest with uniform acceleration. The velocity of the body after t seconds is v. The displacement of the body in last three seconds is (1) 3v/2[(t – 3)] (2) 3v/2[(t + 3)] (3) 3v[1 – 3/2t] (4) 3v[1 + 3/2t]

Answer: (3) 3v[1 - 3/2t] Let a be the uniform acceleration of the body . Then v = at a = v/t____________(1) Displacement is calculated as the... View Article

A ring of radius 1 m is lying on the surface of liquid. It is lifted from the liquid surface by a force of 4 newtons in such a way that the liquid film in it remains intact. What is the surface tension of liquid?

Answer: Surface tension is the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the... View Article

The potential difference V and the current I flowing through an instrument in an AC circuit are given by V = 5cosωt volt, I = 2sinωt Amp . The power dissipated in the circuit is (1) 5 watt (2) 10 watt (3) 2.5 watt (4) 0

Answer: (4) 0 In an AC circuit, the power dissipated in the circuit is given as follows P = Vrms Irms cosϕ The ϕ is the phase difference... View Article

A person is unable to see objects nearer than 50cm. He wants to read a book placed at a distance of 25cm. Find the nature of focal length and power of the lens, he needs for his spectacles.

A person is unable to see objects nearer than 50cm. He wants to read a book placed at a distance of 25cm. Find the nature of focal length and... View Article

Three bulbs A, B and C are connected as shown in the figure. The bulbs B and C are identical. If bulb C is fused, then (1) Brightness of both bulbs A and B will increase (2) Brightness of both bulbs A and B will decrease (3) Brightness of bulb A decrease and that of bulb B increases (4) None of the bulbs will glow

Answer:(3) Brightness of bulb A decrease and that of bulb B increases Bulbs B and C are connected in parallel and bulb A is connected in series... View Article

About which of the following axes moment of inertia of a circular disc is minimum? (1) Axis passing through its centre and perpendicular to its plane. (2) Axis along the diameter. (3) Axis along the tangent and in its own plane (4) Axis along the tangent and perpendicular to its plane.

Answer: (2) Axis along the diameter Moment of inertia is defined as the quantity expressed by the body resisting angular acceleration which is... View Article

An object at a distance of 30 cm from a concave mirror gets its image at the same point. The focal length of the mirror is (1) -30cm (2) +30cm (3) -15cm (4) +15cm

Answer: (3) -15cm If a hollow sphere is cut into parts and the outer surface of the cut part is painted, then it becomes a mirror with its inner... View Article

A conducting sphere of radius r = 20 cm is given a charge q = 16μC. What is electric field E at its centre?

Answer: Given parameters Radius of the sphere (r) = 20cm = 0.2 m Charge (q) = 16μC = 16 × 10-6 C E = ? Electric field can be... View Article

A hot and a cold body are kept in vacuum separated from each other. Which of the following causes decrease in temperature of the hot body? (1) Radiation (2) Convection (3) Conduction (4) Temperature remains unchanged.

Answer: (3) Radiation In the radiation mode, heat can pass through a vacuum, reducing the temperature of the hot body. The physical act of... View Article

What happens to the centripetal acceleration of a revolving body if you double the orbital speed v and half angular velocity ω (1) It remains unchanged (2) It is halved (3) It is doubled (4) It is quadrupled

Answer: (1) It remains unchanged Centripetal acceleration is defined as the property of the motion of an object, traversing a circular path. Any... View Article

In the adjoining figure, AOB is a straight line. Find the value of x. Hence, find ∠AOC, ∠COD and ∠BOD

From the figure we know that ∠BOD and ∠AOD are a linear pair of angles Hence ∠BOD + ∠AOD = 180º It can also be... View Article

In the absence of an electric field, the mean velocity of free electrons in a conductor at absolute temperature (T) is

In the absence of an electric field, the mean velocity of free electrons in a conductor at absolute temperature (T) is zero In the... View Article

Moment of inertia of a rectangular plate about an axis passing through p and perpendicular to the plate is

Moment of inertia is defined as the quantity expressed by the body resisting angular acceleration which is the sum of the product of the mass of... View Article

How to find to find the mean, mode, and median of any set of numbers.

Mean is the most commonly used measure of central tendency. It actually represents the average of the given collection of data. It is applicable... View Article

Let us consider a system of units in which mass and angular momentum are dimensionless. If length has dimension of L, which of the following statement(s) is/are correct? (A) The dimension of force is L^–3 (B) The dimension of power is L^–5 (C) The dimension of linear momentum is L^–1 (D) The dimension of energy is L^–2

The correct options are (A) The dimension of force is L–3 (C) The dimension of linear momentum is L–1 (D) The dimension of... View Article

Assuming the balls to be identical except for difference in colours the number of ways in which one or more balls can be selected from 10 white, 9 green and 7 black balls is

Permutation relates to the act of arranging all the members of a set into some sequence or order. The combination is a way of selecting... View Article

A card is drawn from a well shuffled deck of 52 cards. what is the probability of getting a red queen card

Probability is the measurement of chances – the likelihood that an event will occur. If the probability of an event is high, it is more... View Article

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