# Physics GK Quiz-32

## Physics GK Quiz-32

Physics Multiple Choice Questions (MCQs) Quiz for State and UPSC Civil Services Examinations. Objective Questions on Physics for competitive examinations.

### 621. Two bodies kept at a certain distance feel a gravitational force F to each other. If the distance between them is made double the former distance, the force will be

(1) 2F
(2)1/2F
(3) 4F
(4) 1/4F
621. (4) Gravitational force F G = ´ m m d 1 2 2 where F is the gravitational force, m1 and m2 are the
masses of two objects, G is the universal gravitational constant and d is the distance between the two
objects. Since the gravitational force is inversely proportional to the square of the distance, if the distance between the two bodies is doubled, the force of gravity is reduced to one-fourth its original value.

### 622. Stationary wave is formed by

(1) a transverse wave superposing a longitudinal wave
(2) two waves of the same speed superposing
(3) two waves of same frequency travelling in the same direction
(4) two waves of same frequency travelling in the opposite direction
622. (4) Stationary or standing waves are formed in a medium when two waves having equal amplitude and frequency moving in opposite directions along the same line, interfere in a confined space. Generally, such waves are formed by the superposition of a forward wave and the reflected wave. Both longitudinal and transverse types of waves can form a stationary wave.

### 623. The work done by the string of a simple pendulum during one complete oscillation is equal to

(1) Total energy of the pendulum
(2) Kinetic energy of the pendulum
(3) Potential energy of the pendulum
(4) Zero
623. (4) Work done by the string of the simple pendulum during one complete oscillation is zero. Tension in the string exactly cancels the component parallel to the string. This leaves a net restoring force back toward the equilibrium position as equal to zero.

### 624. The minimum number of forces to keep a particle in equilibrium is

(1) 1
(2) 2
(3) 3
(4) 4
624. (2) When the resultant of all forces acting on a particle is zero, the particle is in equilibrium. The equilibrium of a particle to which a single force is applied may be maintained by the application of a second force that is equal in magnitude and direction, but opposite in sense, to the first force. This second force, which restores equilibrium, is called the equilibrant. Hence, the minimum number of forces to keep a particle in equilibrium is two.

### 625. A system exhibiting S.H.M. must possess

(1) Elasticity as well as inertia
(2) Elasticity, inertia and an external force
(3) Elasticity only
(4) Inertia only
625. (1) Basic conditions to execute simple harmonic motion are: (i) There must be an elastic restoring force acting on the system, (ii) the system must have inertia, and (iii) the acceleration of the system should be directly proportional to its displacement and is always directed to mean position.

### 626. A needle or a pin floats on the surface of water because of

(1) Surface tension
(2) Surface energy
(3) Viscosity
626. (1) The pin or needle floats because of an invisible elastic skin on the surface of the water. This elastic skin is called surface tension. Surface tension of the water leads to forces strong enough to support the needle’s weight.

### 627. Super conductors are substances that

(1) offer minimum resistance to flow of electric current
(2) conduct electricity at low temperature
(3) conduct electricity at high temperature
(4) offer high resistance to the flow of electric current
627. (1) A superconductor is a material that can conduct electricity or transport electrons from one atom to another with no resistance. No heat, sound or any other form of energy is released from the material
when it reaches the temperature at which it becomes superconductive.

### 628. A thin oil film on a water surface appears coloured because of

(1) reflection
(2) interference
(3) diffraction
(4) polarization
628. (2) A thin oil film on a water surface appears coloured because of thin-film interference which involves the interference of light waves reflecting off the top surface of a film with the waves reflecting from the bottom surface. The refractive index of oil is larger than that of water, therefore the reflection on the back side occurs. Contructive interference incident light air oil water.

### 629. The ‘Greenhouse effect’ is mainly due to increase in atmospheric

(1) Ozone
(2) Nitrogen
(3) Sulphur dioxide
(4) Carbon dioxide
629. (4) Carbon dioxide is the primary greenhouse gas that is contributing to recent climate change, 72% of the totally emitted greenhouse gases is carbon dioxide (CO2), 18% Methane and 9% Nitrous oxide (NOx). Carbon dioxide emissions therefore are the most important cause of global warming.

### 630. In a conductor

(1) there is no conduction band
(2) the forbidden energy gap is very wide
(3) the forbidden energy gap is very narrow
(4) the valence band and the conduction band overlap each other
630. (4) In the case of a conductor, there is no forbidden energy gap. The conduction and valence energy bands overlap each other. Obviously, the electrons from the valence band can freely enter the conduction energy band. Conduction energy band Overlap Valence energy band.

### 631. The moment of inertia of a body does not depend upon its

(1) axis of rotation
(2) angular velocity
(3) form of mass
(4) distribution of mass
631. (2) Moment of inertia is the mass property of a rigid body that determines the torque needed for a desired angular acceleration about an axis of rotation. Moment of inertia depends on the shape of the body and the amount and distribution of its mass. It can be found through the sum of moments of inertia of the masses making up the whole object, under the same conditions.

### 632. To open a door easily, the handle should be fixed

(1) near the hinges
(2) away from mid-point opposite to hinges
(3) in the middle
(4) None of these
632. (4) Since Torque = force x distance, to open a door easily, the handle should be fixed at the greatest distance from the hinges. If we pull with same force on a handle that is 2 feet away from the hinges, we will provide twice the torque, so it will be twice as easy to open.

### 633. Optical fibre works on the principle of

(1) refraction
(2) scattering
(3) interference
(4) total internal reflection
633. (4) An Optical Fiber works on the principle of Total Internal Reflection. Light rays are reflected and guided down the length of an optical fiber. The acceptance angle of the fiber determines which light rays will be guided down the fiber.

### 634. The colours of stars depend on their

(1) temperature
(2) distance
(4) atmospheric pressure
634. (1) The colour of a star tells about its temperature, and the temperature depends on some combination of the star’s mass and evolutionary phase.

### 635. The sky appears blue due to

(1) Rayleigh scattering
(2) Mie scattering
(3) Back scattering
(4) None of the above
635. (1) The blue colour of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air. However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky.

### 636. A particle is moving in a uniform circular motion with constant speed v along a circle of radius r. The acceleration-of the particle is

(1) zero
(2)V/r
(3)V/2r
(4)V2r
636. (4) When a particle is moving in a uniform circular motion with constant speed and radius. the acceleration of the particle is given by v2/r. The particle will exhibit centripetal acceleration.

### 637. Which of the following devices can be used to detect radiant heat ?

(1) Liquid thermometer
(2) Six’s maximum and minimum thermometer
(3) Constant volume air thermometer
(4) Thermopile
637. (4) Based on the thermoelectric effect, the thermopile can be used as a heat sensor to measure thermal radiation. A thermopile is made of thermocouple junction pairs connected electrically in series. Thermocouples near the ground measures radiant energy.

### 638. In which one of the following the phenomenon of total internal reflection of light is used ?

(1) Formation of mirage
(2) Working of binoculars
(3) Formation of rainbow
(4) Twinkling of stars
638. (3) When the angle of incidence is greater than the critical angle, no refraction occurs. Instead, the incident beam is reflected, obeying the Law of Reflection. This is called Total internal reflection. In the
formation of a rainbow, Total Internal Reflection occurs at the rear of the raindrop - the water-to-air
interface.

### 639. Period of oscillation of 3 cm microwaves in seconds is

(1) 1 × 1010
(2) 1 × 10–10
(3) 0.01
(4) 0.001
639. (2) The period of oscillation of 3 cm microwaves is 1 x 10-10 (Physics, Volume 1, by Halliday). The period of oscillation is the smallest interval of time in which a system undergoing oscillation returns to the state it was in at the beginning of the oscillation.

### 640. The device used to convert solar energy into electricity is

(1) Photovoltaic cell
(2) Daniell cell
(3) Electrochemical cell
(4) Galvanic cell