191. The ‘Black Box’ of an aeroplane is of-

1. White colour
2. Red colour
3. Black colour
4. Orange colour

Option “4” is correct.
The black boxes are actually painted with a heat-resistant bright orange colour in order to make them easier to find in wreckage resulting from the crash.
192. The Indira Gandhi Atomic Research Centre is located in-

1. Maharashtra
2. Tamil Nadu
3. Uttar Pradesh
4. Karnataka

Option “2” is correct.
Indira Gandhi Centre for Atomic Research (IGCAR) was established in the year 1971 at Kalpakkam (Tamilnadu), under the department of Atomic Energy, Government of India.
193. Photovoltaic cells are:

1. Solar cells
2. Thermal cells
3. Sulphur cells
4. Chemical cells

Option “1” is correct.
The conversion of light energy into electrical energy is based on the phenomenon called photovoltaic effect. A photovoltaic cell is the basic unit of the system where the photovoltaic effect is utilized to produce electricity from light energy. Silicon is most widely used semiconductor material for construction photovoltaic cell.
194. Which of the following is a semiconductor?

1. Plastic
2. Aluminum
3. Wood
4. Germanium

Option “4” is correct.
Germanium and silicon are semiconductor materials.
195. Radioactive substance emits-

1. Alpha rays
2. Beta rays
3. Gamma rays
4. All the above

Option “4” is correct.
Radioactive elements are elements that have an unstable nucleus. When the nuclei are considered unstable, they radiate alpha, beta and Gamma radiation and is converted into a stable element. This type of radiation is invisible for naked eye.
196. What are the links between Dhruva, Purnima and Cirus?

1. They are Indian research reactors
2. They are stars
3. These are names of famous books
4. They are power plants

Option “1” is correct.
Dhruva, Purnima, and Cirus are Indian research reactors.
197. Total internal reflection can take place when light travels from:

1. Diamond to glass
2. Water to glass
3. Air to water
4. Air to glass

Option “1” is correct.
Total internal reflection takes place when a ray of light is travelling from denser to thinner medium and angle of incidence is greater than the critical angle, the ray is completely reflected from surface and meet each other as if the surface is a mirror. So according to options, the situation of option (a) is correct where total internal reflection takes place, it is because diamond is denser than glass.
198. Which one of the following phenomenon is used in optical fibres?

1. Interference
2. Refraction
3. Total internal reflection
4. Polarisation

Option “3” is correct.
The optical fibre is a very thin strand of glass or plastic cable for transmitting light from one point to another. They work on he principle of total internal reflection. There is no loss of signal through an optical fibre.
199. An endoscope is a-

1. Narrow telescope
2. Type of camera
3. Simple microscope
4. None of these

Option “4” is correct.
An endoscope is a medical device consisting of a long, thin, flexible (or rigid) tube which has a light source and a video camera. Images of the inside of the patient’s body can be seen on a screen. It is not suitable to categorize endoscope as a type of a camera.
200. Which instrument is used for measuring humidity in the air?

1. Hydrometer
2. Hygrometer
3. Spectrometer
4. Eudiometer

Option “2” is correct.
A hygrometer is an instrument used to measure the moisture content in the atmosphere which is also called as humidity in the air.
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