271. Why does a fountain pen leak in aeroplane flying at a height?

1. Because of reduced viscosity of the ink in the pen
2. Because of increased viscosity of the ink in the pen
3. Because of higher atmospheric pressure outside the pen
4. Because of lower atmospheric pressure outside the pen

Option “4” is correct.
The atmospheric pressure decreases with altitude because gas molecules which make up the air concentrate near lower altitude in response to Earth’s gravity. Hence, air pressure is low at higher altitudes. Due to this difference in air pressure, the air inside the pen forces the ink to come out.
272. Instrument for measuring time is called _____ .

1. Diagometer
2. Anemometer
3. Durometer
4. Chronometer

Option “4” is correct.
Chronometer is an instrument for measuring time accurately in spite of motion or variations in temperature, humidity, and air pressure.
273. If the radius of the earth decreases and its mass remains the same, then the value of “acceleration due to gravity” will _____ .

1. Decrease
2. Increase
3. Remain the same
4. Become zero

Option “2” is correct.
If the radius of the earth decreases and its mass remains the same, then the value of “acceleration due to gravity” will increase.
274. Earth revolves around Sun. Who was the 1st one to present this theory?

1. Albert Einstein
2. Galileo
3. Copernicus
4. Newton

Option “3” is correct.
Nicolaus Copernicus was a Polish astronomer who put forth the theory that the Sun is at rest near the center of the Universe, and that the Earth, spinning on its axis once daily, revolves annually around the Sun. This is called the heliocentric, or Sun-centered, system. Copernican heliocentrism is the name given to the astronomical model developed by Nicolaus Copernicus and published in 1543.
275. The device used for locating submerged objects under sea is –

1. Sonar
2. Radar
3. Laser
4. Maser

Option “1” is correct.
Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.
276. Which of the following lens is used to minimize Myopia?

1. Convex lens
2. Concave lens
3. Cylindrical lens
4. None of these

Option “2” is correct.
A concave lens is used to remove the defect of myopia.
277. Alternate current is not preferable-

1. To charge storage battery
2. To run/start a electric motor
3. To transmit electric power
4. To heat up electric toaster

Option “1” is correct.
Direct Current is used to charging the batteries with the help of rectifier which converts AC to DC. Thus alternate current is not preferable for it.
278. Which of the following are semiconductors?

1. Silicon
2. Quartz
3. Ceramics
4. Germanium

Choose the correct answer from the following alternatives:

1. 1 and 2
2. 1 and 3
3. 1 and 4
4. 3 and 4

Option “3” is correct.
In solid state electronics, either pure silicon or germanium may be used as the intrinsic semiconductor which forms the starting point for fabrication. Each has four valence electrons but germanium at a given temperature has more free electrons and higher conductivity. Silicon is by far the more widely used semiconductor for electronics because it can be used at much higher temperatures than germanium.
279. Cyclotrons are used to accelerate:

1. Neutrons
2. Protons
3. Atoms
4. Ions

Option “2” is correct.
Cyclotron is a machine used to accelerate charged particle such as alpha particles, deuteron, proton etc. up to a very high speed.
280. Which one of the following can be used to confirm whether drinking water contains a gamma emitting isotope or not?

1. Microscope
2. Lead plate
3. Scintillation counter
4. Spectrophotometer

Option “3” is correct.
Scintillation counter is an instrument for detecting ionizing radiation by using the excitation effect of incident radiation. Radiation on a scintillator material and detecting the resultant light pulses.
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