In the NDA & NA (II) 2017 Exam, the question from physics covered key areas such as – Units, light, radio activity, etc. For the benefit of the NDA aspirants, Jagran Josh is providing geography questions, answers along with detailed explanation.
1. The symbol of SI unit of inductance is H. It stands for
The henry (symbol: H) is the SI derived unit of electrical inductance. The unit is named after Joseph Henry (1797–1878), the American scientist who discovered electromagnetic induction independently of and at about the same time as Michael Faraday (1791–1867) in England.
2. Electron emission from a metallic surface by application of light is known as
(a) Thermionic emission
(b) Photoelectric emission
(c) High field emission
(d) Autoelectronic emission
Ans. (b) Photoelectric emission
Electron emission from a metallic surface by the application of light is known as photoelectric emission. When a beam of light strikes the surface of cathode normally made of potassium, Sodium the energy of photons of light is transfer to the free electrons of cathode.
3. How long does light take to reach the Earth from the Sun?
(a) About 4 minutes
(b) About 8 minutes
(c) About 24 minutes
(d) About 24 hours
Ans.(b) About 8 minutes
Sunlight travels at the speed of light. Photons emitted from the surface of the Sun need to travel across the vacuum of space to reach our eyes. The short answer is that it takes sunlight an average of 8 minutes and 20 seconds to travel from the Sun to the Earth.
4. Radioactivity is measured by
(a) GM Counter
Ans. (a) GM Counter
The Geiger counter is an instrument used for measuring ionizing radiation used widely in applications such as radiation dosimetry, radiological protection, experimental physics and the nuclear industry.
5. The mirrors used as rear-view mirrors in vehicles are
Ans. (b) convex
An image formed in a convex mirror is smaller than an image in a plane (flat) mirror. Because the image is smaller, more image can fit onto the mirror, so a convex mirror provides for a larger field of view than a plane mirror. This is why they are useful. They are used whenever a mirror with a large field of view is needed. For example, the passenger-side rear view mirror on a car is convex
6. Which one of the following waves is used for detecting forgery in currency notes?
(a) Ultraviolet waves
(b) Infrared waves
(c) Radio waves
Ans. (a) Ultraviolet waves
UV counterfeit currency detectors are used to detect special inks in the currency notes that only appear under the proper wavelength of UV light. When exposed to UV light, the UV ink changes its appearance and becomes visible to the human eye.
7. Concave mirror is used in headlights of vehicles, because it
(a) focuses light from the bulb onto nearby vehicles
(b) sends parallel rays
(c) fits well into the shape of the headlight
(d) is cheaper than other mirrors
Some uses of a concave mirrors, are used in vehicle headlights to send paralell rays because it allows the light rays to be focused as a single beam and give more power to the light, that makes it more efficient for seeing and to be seen by others.
8. If some object is weighed when submerged in water, what will happen to its weight compared to its weight in air?
(c) Remain exactly the same
(d) Increase or decrease cannot be predicted
Ans. (b) Decrease
The weight of an object is defined by its mass and the gravity. In mathematical terms, it is calculated as w=mg; w is weight, m is mass and g is gravity acting on the object.
Any object weighs the same in air as well as in water. But in water (due to its density of 1000 kg/m⊃3;), an additional buoyant force acts on the ball in a direction opposite to the direction in which the weight of the ball acts. Thus, if the weight of the ball acts downwards, buoyant force acts upwards. These two forces work together to make it seem as though the ball weighs less in water.
9. Light year is a measure of
(c) total amount of light falling on the Earth in a year
(d) average intensity of light falling on the Earth in a year
Ans. (b) distance
Light year is a measure of distance. It is a unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.4607 × 1012 km (nearly 6 million million miles).
10. Which one of the following statements about energy is correct?
(a) Energy can be created as well as destroyed.
(b) Energy can be created but not destroyed.
(c) Energy can neither 'be created nor destroyed
(d) Energy cannot be created but can be destroyed
Ans. (c) Energy can neither 'be created nor destroyed
The first law of thermodynamics, also known as Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another
Best wishes from Jagran Josh!!!!