DSSSB PGT Physics Mock Test - 5 - DSSSB TGT/PGT/PRT MCQ

A freely falling body observes a constant downwards force of gravity which hence applies a constant downward acceleration upon the body.

Explanation:Vector addition is commutative, just like addition of real numbers. If you start from a point say P,  you end up at the same spot no matter which displacement (a or b) you take first. The head-to-tail rule yields vector c for both a + b and b + a.

Both statements are independently true but 2 is not the correct explanation of 1.
The reason for statement 1 is that while pulling, a component of force reduces the normal reaction and hence reduces the friction force.
 

F. B. D. of block with respect to wedge.

Railway tracks are banked at curves to help the train negotiate the curve safely. The banking of the tracks ensures that the necessary centripetal force is provided by the horizontal component of the normal reaction force from the track. This reduces the reliance on friction between the train wheels and the track, allowing trains to travel safely around curves at higher speeds.

F=k x (compression in string).
X=L.
a=LT^-2.
F=ma.
ma= k L.
LT^-2/L=k/m.
T^-2=k/m.

As the relative velocity of the satellite with respect to the earth is zero, it appears stationary from the Earth surface and therefore it is called is geostationary satellite or geosynchronous satellite.

Bernoulli's theorem, in fluid dynamics, relation among the pressure, velocity, and elevation in a moving fluid (liquid or gas), the compressibility and viscosity (internal friction) of which are negligible and the flow of which is steady, or laminar.

In this process, heat is transferred in the liquid and gases from a region of higher temperature to a region of lower temperature. Convection heat transfer occurs partly due to the actual movement of molecules or due to the mass transfer

The second law of thermodynamics gives a fundamental limitation to the efficiency of a heat engine and the coefficient of performance of a refrigerator. It says that the efficiency of a heat engine can never be unity or 100%, this implies that the heat released to the cold reservoir can never be made zero.
For a refrigerator the second law says that the coefficient through performance can never be infinite, this implies that the external work can never be zero.

For triatomic gas γ = 4/3

Explanation:

At const volume, 

Q = 500 J

Q=nCPΔT

500=1×2.5×8.31ΔT

ΔT=24.06

W=nRΔT=1×8.31×24.06=200J

The bob of a pendulum moves in such a way that it repeats its positions several time but alternately the time gap between these positions is always equal which proves that the motion of a pendulum is oscillatory.

B because of constructive interference.

Electric flux, Φ = −1.0 × 10³ N m²/C

Radius of the Gaussian surface,

r = 10.0 cm

Electric flux piercing out through a surface depends on the net charge enclosed inside a body. It does not depend on the size of the body. If the radius of the Gaussian surface is doubled, then the flux passing through the surface remains the same i.e., −10³ N m²/C.

Electric flux is given by the relation,

qϕ=q∈0

Where,

q = Net charge enclosed by the spherical surface

∈₀ = Permittivity of free space = 8.854 × 10⁻¹² N⁻¹ C² m⁻²

∴ qq=ϕ∈0

= −1.0 × 10³ × 8.854 × 10⁻¹²

= −8.854 × 10⁻⁹ C

= −8.854 nC

Therefore, the value of the point charge is −8.854 nC.

Since the charge –q is moving in elliptical orbit so to make its motion stable the total angular momentum of the charge is constant since it experience a centripetal force from the charge +Q so it follow the motion as the motion of earth around sun.

 V = Q/(4πεr), where r = 1m
V = (2 X 10^-9)/(4πε x 1) = 18 volts.

EMF is equal to potential difference between plates when the battery is not connected to any external circuit. 
Potential difference is due to the charge accumulation on the plates. So, EMF produces a potential difference between the two terminals which drives the current.

TV signals being of high frequency are not reflected by the ionosphere. Therefore, to reflect these signals, satellites are needed. That is why, satellites are used for long distance TV transmission.
 Most long-distance shortwave (high frequency) radio communication—between 3 and 30 MHz—is a result of skywave propagation.
This 3-30 MHz is a range of frequencies which are used in sky waves propagation so that the ionosphere is capable of reflecting it.

Maxwell’s Fourth Equation
It is based on Ampere’s circuital law. To understand Maxwell’s fourth equation it is crucial to understand Ampere’s circuital law,
Consider a wire of current-carrying conductor with the current I, since there is an electric field there has to be a magnetic field vector around it. Ampere’s circuit law states that “The closed line integral of magnetic field vector is always equal to the total amount of scalar electric field enclosed within the path of any shape” which means the current flowing along the wire(which is a scalar quantity) is equal to the magnetic field vector (which is a vector quantity)

Brewster's angle is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection. When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore perfectly polarized.
So the angle of incidence would be 60°

The number of electrons ejected can be measured as a function of intensity.
Intensity is equal to energy per unit time per unit area.
Keeping frequency constant, increasing intensity will increase energy thus increase of ejected electrons.
Thus,
Number of ejected photoelectrons will increase with increase in intensity of light. 

Lines in the spectrum were due to transitions in which an electron moved from a higher-energy orbit with a larger radius to a lower-energy orbit with smaller radius. The orbit closest to the nucleus represented the ground state of the atom and was most stable; orbits farther away were higher-energy excited states.

Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways.

Given that 90% is left un-decayed after time 't'.
Hence, 10% decays in time 't'.
Initially assume that the amount of substance is 'x'
After time 't' 10% is decayed.
i.e. Amount of substance left =0.9x
After further time 't' another 10% is decayed.
i.e. 0.1×0.9x is decayed 
Leaving behind 0.81x.
Hence after time 2t we see that 0.19x has decayed, which is 19%.
 

When a p−n junction is formed, some of the free electrons in the n region diffuse across the junction and combine with holes to form negative ions. In doing so they leave behind positive ions at the donor impurity sites. Similarly, holes from p side diffuse to the n side and thus form a layer called diffusion layer at the junction.
So the depletion region is caused by the diffusion of charge carriers.
 

There are two depletion regions in a transistor, since there are two PN junctions.

Number of significant figures are 3, because 103 is decimal multiplier.