Which of the following is / are correct statements about the Millimeter waves, sometimes seen in news?
- These are among the highest radio frequency band
- They have higher wavelength than Microwaves
- They are most notably used in security appliances
Select the correct option from the codes given below:
[A] Only 1 & 2
[B] Only 2 & 3
[C] Only 1 & 3
[D] 1, 2 & 3
Hide Answer
Correct Answer: C [ Only 1 & 3]
Notes:
Millimeter Waves correspond to the EHF Band which runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low (or far) infrared light, also referred to as terahertz radiation. This band has a wavelength of ten to one millimetre. The Microwaves have wavelength of from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. Thus statement 2 is incorrect.
2.Which among the following is / are correct statements?
1. The images produced by Concave Mirrors are always real images
2. The images produced by Flat Mirrors are always virtual images
3. Converging Lens can produce virtual as well as real images
Select the correct option from the codes given below:
[A] Only 1 is correct
[B] Only 2 is correct
[C] Only 1 & 2 are correct
[D] Only 2 & 3 are correct
Hide Answer
Correct Answer: D [ Only 2 & 3 are correct]
Notes:
Real images can be produced by concave mirrors and converging lenses. But a converging lens and concave mirror are also capable of producing virtual images if the object is within the focal length. Thus statement 1 is incorrect, while statement 3 is correct. Flat mirrors can never produce real image because, rays never really converge, so statement 2 is correct.
3.With reference to the Sound waves, which among the following is / are correct statements?
1. The frequency determines the pitch of a sound, and the amplitude determines the intensity (or loudness)
2. Frequency is proportional to amplitude
Select the correct option from the codes given below:
[A] Only 1
[B] Only 2
[C] Both 1 & 2
[D] Neither 1 nor 2
Hide Answer
Correct Answer: A [ Only 1]
Notes:
The frequency determines the pitch of a sound, and the amplitude determines the intensity (or loudness). Pitch and loudness are independent. A sound can be soft and low pitched, soft and high pitched, loud and low pitched, or loud and high pitched; there’s no connection.
4.Which of the following comparisons of different types of lights is / are correct?
- Ultraviolet light has a higher energy and shorter wavelength than visible light
- Orange light has a lower frequency and longer wavelength than blue light
Select the correct option from the codes given below:
[A] Only 1
[B] Only 2
[C] Both 1 & 2
[D] Neither 1 nor 2
Hide Answer
Correct Answer: C [ Both 1 & 2]
Notes:
Gamma rays and X-rays are very high-energy, short-wavelength radiations. Ultraviolet light has a higher energy and shorter wavelength than visible light. Within the visible spectrum, the colors are—in order of increasing frequency—ROYGBV, so orange light (“O”) has a lower frequency—and thus a longer wavelength—than blue light (“B”).
5.In terms of Physics, which among the following situations result in work done?
- Brakes are applied to a moving vehicle and vehicle stops
- A ball is projected vertically upward and it comes back due to force of gravity
- A body moves in a circular path
Select the correct option from the codes given below:
[A] Only 1 & 2
[B] Only 2 & 3
[C] Only 1 & 3
[D] 1, 2 & 3
Correct Answer: A [ Only 1 & 2]
Notes:When a body is acted upon by a force, there are two conditions when work done is zero. Firstly, the force must not cause displacement in its own direction; secondly, the force must act at right angle to direction of displacement. However, the work can be positive or negative. Positive work is done, when the angle between the direction of force applied and the displacement of body is zero. For example, when a horse pulls a cart or an engine pulls a train, the positive work is done. Negative work is done, when the angle between the direction of the force applied and the displacement is 180° i.e., the displacement is in a direction opposite to the force. For example, when brakes are applied to a moving vehicle, the work done by the applied force is negative. Similarly, when a ball is projected vertically upward, the work done by the force of gravity is negative. When a body moves in a circular path, no work is done. It is because, the centripetal force acting on the body is always at right angles to the displacement of the body along the circular path.
Thus, cos 90° = 0
So, in the expression
W = F cos 90° × S = 0 × S = Zero
At the same time, we note that when satellite revolves around the earth in a circular orbit. Work done by the force due to gravity is zero, because it acts at right angles to the direction of displacement of the satellite
6.The ultraviolet radiations find their applications in which of the following?
- simulate the human body to produce vitamin-d
- distinguish between fake and real diamonds
- detect any alteration in the bank cheques
- detect forged currency notes
- relieve pain from swollen joints
Select the correct option from the codes given below:
[A] Only 1, 2 & 3
[B] Only 2, 3, 4 & 5
[C] Only 1, 2, 3 & 4
[D] 1, 2, 3, 4 & 5
Correct Answer: C [ Only 1, 2, 3 & 4]
Notes:
Controlled exposure of ultraviolet radiations stimulates the body to produce vitamin D. Vitamin D is then used by body for strengthening bones and teeth. Kindly note that Infra-red waves are used by doctors to relieve pain from swollen joints.
7.Which of the following is/are a vector quantity?
- Temperature
- Work
- Kinetic Energy
- Momentum
- Power
Select the correct option from codes given below:
[A] 2 and 4 Only
[B] 4 Only
[C] 2, 3, 4 and 5 Only
[D] 1, 2, 3, 4 and 5
Correct Answer: B [ 4 Only]
Notes:
A scalar quantity is one which has only magnitude. A vector quantity has both magnitude and direction.
Temperature is a comparative measure of hot or cold and is expressed in Celsius, Fahrenheit and kelvin, which represents only magnitude and no direction.Hence temperature, is a scalar quantity.
Work is again a scalar quantity because W=F.S where F is force which is a vector quantity and S is displacement which is again a vector quantity.So, dot product of two vector quantity is a scalar quantity.
Power is again a scalar quantity as Power is defined as rate of work done
P=W/T, A scalar quantity divided by scalar is scalar.
Momentum is M=m.v where m is the mass of the body which is scalar quantity and v is the velocity which is vector quantity. Dot product of scalar and vector is vector.
K.E=1/2 mv^2, where v^2 is the dot product of two vector quantity and hence is scalar. Dot Product of two vector quantity is scalar.
8.Due to which of the following phenomena, the coloured glass appears white when crushed into fine powder?
[A] Total Internal Reflection
[B] Diffraction
[C] Scattering
[D] Refraction
Correct Answer: C [ Scattering]
Notes:
When the glass is crushed into fine powder the light incident is totally scattered without the absorption so due to the composite light crushed glass appears white.
9.Consider the following statements:
- Speed of sound increases with increase in density of the medium
- Speed of sound increases with increase in temperature of the medium
Which of the above statements is/are correct?
[A] 1 Only
[B] 2 Only
[C] Both 1 & 2
[D] Neither 1 nor 2
Correct Answer: B [ 2 Only]
Notes:
When the elasticity of the medium increases the density decreases and it increases the sound speed. Higher temperatures lower the density of a medium, which puts less resistance on the sound waves.
10.Who among the following is credited to work for the unification of electricity, magnetism and optics field of Physics?
[A] James Clerk Maxwell
[B] Michael Faraday
[C] Haris Christian Oersted
[D] Isaac Newton
Correct Answer: A [James Clerk Maxwell]
Notes:
James Clerk Maxwell made the efforts for the unification of electricity, magnetism and optics field of Physics. He showed that light is an electromagnetic wave. James Clerk Maxwell was a Scottish mathematician, physicist and is known best for his mathematical work on electromagnetism and on the behaviour of gases.