# Physics GK Quiz-34

## Physics GK Quiz-34

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

### 661. A wavelength of 0.3 m is produced in air and it travels at a speed of 300 m/s. Then it will be an

(1) Audible wave
(2) Infrasonic wave
(3) Ultrasonic wave
(4) Microwave
661. (1) The formula of frequency is: f = c / ë = wave speed c (m/s) / wavelength ë (m), where f: frequency, c: wave speed, and ë: wavelength. As per the question, f = 300/0.3 = 1000 cycles/ seconds = 1000 Hz = 1 KHz Sound waves with frequencies above 20 KHz are called Ultrasonic; those below 20 Hz are called Infrasonic. Sound waves with frequencies between 20 Hz to 20,000 Hz are called audible waves.

### 662. Water has maximum density at

(1) 100°C
(2) 0°C
(3) 4°C
(4) 273°C
662. (3) The maximum density of water occurs at 4 °C because at this temperature two opposing effects are in balance. Water is an exceptional compound that has a lower density in the solid phase than the liquid phase (i.e., ice floats on water). This is actually due to the ion nature of water in the liquid phase, which packs the molecules tightly together.

### 663. If a body moves with a constant speed in a circle

(1) no work is done on it
(2) no force acts on it
(3) no acceleration is produced in it
(4) its velocity remains constant
663. (4) A body moving with a constant speed in a circle is an example of uniform circular motion. The velocity vector is constant in magnitude but changing in direction. Since velocity is a vector quantity that has both magnitude and direction, a change in either the magnitude or the direction constitutes a change in the velocity which leads to change in acceleration.

### 664. The waves used in sonography are

(1) Micro waves
(2) Infra-red waves
(3) Sound waves
(4) Ultrasonic waves
664. (4) Sonography is an ultrasound-based diagnostic imaging technique used for visualizing internal body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. In physics, 'ultrasound' refers to sound waves with a frequency too high for humans to hear.

### 665. Which of the following is a scalar quantity ?

(1) Velocity
(2) Force
(3) Angular momentum
(4) Electrostatic potential
665. (4) The electrostatic potential at any point in an electric field is defined as the work done in bringing a unit positive charge from infinity to that point against the electric force of the field. It is given by, V = W/q, where V is the potential, W is work done, and q the charge. Because work and charge both are scalar quantity, electrostatic potential is also a scalar quantity

### 666. Which of the following is not a vector quantity ?

(1) Speed
(2) Velocity
(3) Torque
(4) Displacement
666. (1) Speed is a scalar quantity that refers to “how fast an object is moving.” Speed can be thought of as the rate at which an object covers distance. It does not keep track of direction. In contrast, velocity is a vector quantity as it is direction aware.

### 667. An object with a constant speed

(1) is not accelerated
(2) might be accelerated
(3) is always accelerated
(4) also has a constant velocity
667. (1) Acceleration is defined as the rate at which an object changes its velocity. An object is accelerating if it is changing its velocity. An object with constant speed will have no acceleration as the speed is uniform.

### 668. A man in a train moving with a constant velocity drops a ball on the platform. The path of the ball as seen by an observer standing on the platform is

(1) A straight line
(2) A circle
(3) A parabola
(4) None of these
668. (3) In the reference frame of the platform the ball has initial horizontal velocity equal to the velocity of the train. The vertical direction is the same observed on the train because both observers agree that gravity is acting on the ball causing an acceleration g. But, in the platform’s reference frame it already had x-velocity, and the resultant path is a parabola.

### 669. Which of the following is responsible for permanent hardness of water ?

(1) magnesium bicarbonate
(2) sodium chloride
(3) calcium sulphate
(4) calcium bicarbonate
669. (3) Permanent hardness is caused by dissolved calcium sulfate (which is not removed by boiling). Hard water contains dissolved magnesium and calcium ions. These make it more difficult for the water to form lather with soap. Temporary hardness is caused by dissolved calcium hydrogen carbonate (which is removed by boiling)

### 670. An electron microscope gives higher magnifications than an optical microscope because :

(1) The velocity of electrons is smaller than that of light
(2) The wavelength of electrons is smaller as compared to the wavelength of visible light
(3) The electrons have more energy than the light particulars
(4) The electron microscope uses more powerful lenses
670. (2) An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. Because the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, the electron microscope has a higher resolving power than a light microscope and can reveal the structure of smaller objects.

### 671. The first law of thermodynamics is simply the case of

(1) Charle’s law
(2) Newton’s law of cooling
(3) The law of heat exchange
(4) The law of conservation of energy
671. (4) The first law of thennodynamics is a version of the law of conservation of energy for thermodynamic systems. It states that the change in the internal energy of a system is equal to the heat added to the system plus the work done on the system.

### 672. Total internal reflection can not take place when light goes from :

(1) glass to water
(2) water to glass
(3) water to air
(4) glass to air
672. (2) For total internal reflection to occur the light must travel from a dense medium to a less dense medium (e.g. glass to air or water to air). It will not happen for light traveling from water (n=1.333) towards glass (n=1.52).

### 673. Hertz is a unit for measuring

(1) Intensity of waves
(2) Frequency of waves
(3) Wavelength
(4) Clarity of waves
673. (2) Hertz (symbol Hz) is the unit of frequency of waves in the International System of Units (SI). It is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide conclusive proof of the existence of electromagnetic waves.

### 674. Vehicles use _____ to see the objects coming from behind.

(1) Concave lens
(2) Convex lens
(3) Convex mirror
(4) Concave mirror
674. (2) Convex mirror is used in rear view mirror of vehicles; so that the driver can see the traffic coming from behind. The field of view is widest in case of a convex mirror, which enables it to show a wider area from behind.

### 675. The rice is cooked more quickly in a pressure cooker because

(1) it is covered.
(2) less quantity of water is used.
(3) None of these
(4) water boils at a higher temperature under pressure.
675. (4) The rice can be cooked faster in a pressure cooker since the boiling point of water increases with pressure. In general, the higher the temperature of the water, the faster the food will cook. The temperature of the water in a pressure cooker is higher than temperature of the water in an open pot.

### 676. It is easy to burst a gas-filled balloon with a neelde than with a nail. It is because

(1) nail is more longer than needle.
(2) nail exerts more pressure than needle on the balloon.
(3) needle exerts more pressure than nail on the balloon.
(4) gas is reactive with the needle.
676. (3) It is easy to burst a gas-filled balloon with a needle than with a nail because the needle applies more pressure than nail. Besides, the application of the pressure is on a small surface area than in the case of nail. In the case of needle, it is a very tiny area at the tip of the needle, so only a little force gives a lot of pressure (pressure = force/area).

### 677. Ice is packed in saw dust because

(1) saw dust will not get melted easily.
(2) saw dust is poor conductor of heat.
(3) saw dust is a good conductor of heat.
(4) saw dust does not stick to the ice.
677. (2) Ice needs to absorb heat energy to melt and become water (called latent heat of fusion). Since sawdust is a poor conductor of heat, it takes more time for the ice to absorb the required heat energy. This allows ice to remain in solid state for more time when packed in saw dust.

### 678. The Dynamo converts

(1) Electrical Energy into Mechanical Energy
(2) Mechanical Energy into Magnetic Energy
(3) None of these
(4) Mechanical Energy into Electrical Energy
678. (4) Dynamo is a device for converting mechanical energy into electrical energy, especially one that produces direct current. It uses electromagnetic principles to convert mechanical rotation into a pulsing direct electric current through the use of a commutator.

### 679. A Fuse wire is characterised by

(1) High resistance and low melting point
(2) High resistance and high melting point
(3) Low resistance and high melting point
(4) Low resistance and low melting point
679. (4) A fuse is a type of low resistance resistor that acts as a sacrificial device to provide over current
protection, of either the load or source circuit. Low resistance causes the fuse wire to melt if a current
more than the safe current for the appliance starts flowing through the circuit. Besides, the wire of fuse
has very low melting point. When high current flows through the circuit due to overloading or a short circuit, the wires gets heated and melts. As a result, the circuit is broken and current stops flowing.

### 680. Burns caused by steam are much severe than those caused by boiling water because

(1) Steam pierces through the pores of body quickly
(2) Steam has latent heat
(3) Steam is gas and engulfs the body quickly
(4) Temperature of steam is higher