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# Part 034 – Physics Previous Year Questions

Q1. On a cold day when the room temperature is 15°C, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15°C, because :
(a) metals have higher thermal capacity than plastics
(b) plastics have a lower density than metals
(c) metals are good conductors of heat
(d) plastics have a higher thermal conductivity than metals
Ans: (c) On a chilly day, the room temperature is lower than our body temperature. Since metals have a higher coefficient of thermal conductivity than plastic, they are better conductor of heat than plastic. So, when we touch the metal cap and the plastic body of a pen, heat from our fingers will flow to the metal cap much more quickly than to the plastic body.

Q2. Copper wires are generally used for electrical power transmission instead of iron wire because :

(a) copper is cheaper than iron
(b) copper is lighter than iron
(c) copper is a better conductor of electricity than iron
(d) copper can take higher power than iron
Ans: (c) Copper is generally preferred for electrical power transmission instead of iron because of its high electrical conductivity and low resistivity. The conductivity (in (S/m) at 20 °C) of copper is 5.96×107, while that of iron is 1.00×107. Among metals, silver has the highest electrical conductivity of 6.30×107, but it is not used commonly due to its high cost.

Q3. Transformer is a device to convert

(a) D.C. to A.C.
(b) Low voltage D.C. into high voltage D.C.
(c) Low voltage A.C. into high voltage A.C.
(d) Mechanical energy into Electrical energy
Ans: (c) A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling with no moving parts. It converts high voltage AC into low voltage AC and vice-versa. It is based upon the principle of mutual induction. Transformers alone cannot convert AC to DC or DC to AC; besides, they cannot change the voltage or current of DC.

Q4. Quality of a musical note depends on

(a) Fundamental frequency
(b) Amplitude of the wave
(c) Harmonics present
(d) Velocity of sound in the medium
Ans: (c) Sound “quality” or “timbre” describes those characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness. Timbre is mainly determined by the harmonic content of a sound and the dynamic characteristics of the sound such as vibrato and the attack-decay envelope of the sound. Harmonic content is the most important of these.

Q5. The reverse effect of X–ray emission is

(a) Raman effect
(b) Compton effect
(c) Zeeman effect
(d) Photoelectric
Ans: (d) When fast moving electrons strike on high atomic weight substance, X – ray is produced. In contrast, Photoelectric effect takes place when radiation of sufficient frequency incident on the metal surface and electrons are emitted. Hence, X – ray is the inverse phenomenon of photoelectric effect.

Q6. The group of solar cells joined together in a definite pattern is called a

(a) Battery
(b) Solar heater
(c) Solar cooker
(d) Solar cell panel
Ans: (d) A single solar cell can produce only a small amount of electricity. In those cases where more electrical power is needed, a large number of solar cells are joined in series. This group of solar cells is called a ‘solar cell panel’. Thus, a solar cell panel consists of a large number of solar cells joined together in a definite pattern.

Q7. One nanometer is equal to ______ meters.

(a) 10 raised to the power (-3)
(b) 10 raised to the power (-6)
(c) 10 raised to the power (-9)
(d) 10 raised to the power (-12)
Ans: (c) A nanometer is a unit of spatial measurement that is 10-9 meter, or one billionth of a meter. It is often used to express dimensions on an atomic scale. It is commonly used in nanotechnology, the building of extremely small machines.

Q8. What is the unit of relative density?

(a) kg/m (b) kg/m2
(c) kg/m3
(d) It has no unit
Ans: (d) Relative density is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material.So, it is a dimensionless quantity and has no unit.

Q9. Acceleration is

(a) Inversely proportional to force
(b) Inversely proportional to mass
(c) Directly proportional to mass
(d) Directly proportional to force
Ans: (a) Acceleration, in physics, is the rate of change of velocity of an object with respect to time. An object’s acceleration is the net result of any and all forces acting on the object, as described by Newton’s Second Law. Newton’s second law of motion states that acceleration is directly proportional to net force when mass is constant.

Q10. Vegetables are cooked in lesser time by adding a pinch of salt while cooking because

(a) boiling point of water increases
(b) latent heat of vaporization of water decreases
(c) latent heat of vaporization of water increases
(d) boiling point of water decreases
Ans: (a) Adding salt raises the boiling point of water, which allows food to cook at higher temperature. The higher the temperature, the higher the rate of heat transfer between the food and water, thus it cooks more quickly.

Q11. Hydraulic brakes in automobile work on

(a) Poiseuille’s principle
(b) Pascal’s principle
(c) Archimedes’ principle
(d) Bernoulli’s principle
Ans: (b) The hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically containing glycol ethers or diethylene glycol, to transfer pressure from the controlling mechanism to the braking mechanism. It works on the principle of Pascal’s law which states that “pressure at a point in a fluid is equal in all directions in space”. When pressure is applied on a fluid it travels equally in all directions so that uniform braking action is applied on all wheels.

Q12. The fuse in an electric circuit is connected in

(a) series with neutral
(b) parallel to live
(c) parallel to neutral
(d) series with live
Ans: (d) A fuse wire is a safety wire connected in series with the live wire that has high resistivity and low melting point. Fuses are always connected in series with the component(s) to be protected from overcurrent. In case of any large current supply or malfunctioning in the electric connections, it melts and breaks the electric circuit.

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