381. Energy conservation means-

1. Generation and destruction of energy
2. Energy could be created
3. Energy could not be created but destroyed
4. Energy can neither be created nor destroyed

Option “4” is correct.
Law of Conservation of Energy means Energy can neither be created nor be destroyed, rather it can only be transformed from one form to another.
382. Which one of the following is not a property of electromagnetic waves?

1. Electromagnetic waves do not show interference and diffraction.
2. Oscillating electric field and magnetic field are perpendicular to each other
3. Electromagnetic waves are transverse waves
4. Electromagnetic waves do not require a medium to propagate

Option “1” is correct.
Electromagnetic waves are propagated by oscillating electric and magnetic fields oscillating at right angles to each other. They are not deflected by electric or magnetic field. They can show interference or diffraction, are transverse waves, may be polarized and need no medium of propagation.
383. What was invented by Zacharias Jansen?

1. Jet Engine
2. Radium
3. Microscope
4. Electric Lamp

Option “3” is correct.
Zacharias Janssen was a Dutch spectacle-maker from Middelburg associated with the invention of the first Optical telescope. He is also credited for inventing the first truly compound microscope.
384. Super cooling is cooling of liquid _____.

1. Below melting point
2. Below freezing point
3. At melting point
4. Above melting point

Option “2” is correct.
Super cooling is the process of chilling a liquid below its freezing point, without it becoming solid.
385. Sextant is an instrument used in which of the following?

1. Cloud cover
2. Navigation
3. Agriculture
4. Medical treatment

Option “2” is correct.
The sextant is an instrument used to measure angles. Mainly used at sea, the tool is so named because its arc is one sixth of a circle – 60 degrees.
386. During the motion of a projectile fired from the earth surface, _______

1. Its kinetic energy remains constant
2. Its momentum remains constant
3. Vertical component of its velocity remains constant
4. Horizontal component of its velocity remains constant

Option “4” is correct.
Since, the projectile is fired at an angle, its velocity can be split into two components – horizontal(Vx) and vertical(Vy).
Vx=v∗cosϕ
Vy=v∗sinϕ
Gravity is the only force acting on it. And it is acting downwards,so only the vertical component of the velocity is affected by this and the horizontal component remains constant.
387. Which of the following waves cannot be polarised?

1. Radio
2. Ultra violet
3. Infrared
4. Ultrasonic

Option “4” is correct.
Ultrasonic waves cannot be polarised,ultrasonic wave is an example of sound
wave and it cannot be polarised.
388. Which of the following is indicated by the colour of a star?

1. Weight
2. Distance
3. Temperature
4. Size

Option “3” is correct.
The color of a star which varies from bluish white and yellow to orange and red is primarily due to its composition and effective temperature.
389. An anemometer measures which of the following

1. Speed of light
2. Speed of wind
3. Speed of water current
4. Speed of satellites

Option “2” is correct.
An anemometer is a device that is used to measure wind speed. There are many different types of anemometers suited for different environments.
390. Satellite is kept moving in its orbit around the Earth; it is due to-

1. Centrifugal force
2. Centripetal force
3. Gravitational force or lack of it
4. Some other forces

Option “2” is correct.
Centripetal force is a real force that counteracts the centrifugal force and prevents the object from “flying out,” keeping it moving instead with a uniform speed along a circular path.
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