DSSSB PGT Physics Mock Test - 1 - DSSSB TGT/PGT/PRT MCQ

The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres or 5.88 trillion miles. As defined by the International Astronomical Union, a light-year is the distance that light travels in vacuum in one Julian year. 

At the highest point of its flight, the vertical component of velocity is zero and the only horizontal component is left which is u_x = u cosθ
Given θ = 45⁰

Solving Eqs. (i), (ii) and (iii), A = 5N, B = 13N

By conservation of momentum we get the speed of the bigger part let say, v = 1 x90 / 3
Hence we get v = 30
Thus the total KE of the system after collision is ½ (3 X 900 + 1 X 8100)
Thus KE = ½ (10800) = 5400
Now  if we apply WET to the system, as no external force has acted upon it, we get
W = ΔKE
= 5400 - 0
= 5.4 kJ

Yes because there is absence of any external force or torque so angular momentum will remain constant
here outstretching the hands means internal forces are working.. so moment of inertia increases in this case and to make angular momentum constant when angular velocity decreases.

M=9x10^-31Kg,r=4.5x10^-10
V=8x10⁵m/s
L=mvr
  =9x10^-31 x 4.5 x 10^-10 x 8 x 10⁵ = 3.24 x 10^-34 kgm²s^-1

We know, the gravitational force 
,
This is valid when R is the centre to centre distance between the two masses M and m.
At a distance r < R, the mass of Earth cannot be taken as M.

The new mass (M'):
The mass of earth will be contained for a radius r. Let us assume that the mean density of the earth is ρ and that earth is a sphere with a radius equal to the distance r. We know, mass = density × volume

Therefore the gravitational force, F = 

Hence the gravitational force, F ∝ r

According to Newton's Third Law of Motion, every action has an equal and opposite reaction. This law applies to the gravitational forces between two bodies as well.

The gravitational force with which the Earth attracts the Moon is equal to the gravitational force with which the Moon attracts the Earth. This is because the forces are action and reaction pairs, as described by Newton's Third Law.

Therefore, if the Earth attracts the Moon with a gravitational force of 10²⁰ N, then the Moon attracts the Earth with the same gravitational force of 10²⁰ N.

Hence, the correct answer is b. 10²⁰ N.

Solution:

• The first law of thermodynamics states: dQ = dU + dW.
• In an isothermal process, the temperature remains constant.
• This means the change in internal energy (dU) is zero because internal energy is a function of temperature.
• Thus, all the heat supplied (dQ) is used to do work (dW).
• According to the second law of thermodynamics, not all heat can be converted to work, but in this ideal case, internal energy does not increase.

Extensive variable →H (enthalpy), E (Internal energy) and Mass. Since these variables depend on the amount of substance or volume or size of the system.

y₁ = A₁ sin wt

y₂ = A₂ cos (wt + f)

Now, y₂ can be rewritten as A₂ sin (wt + f + π/2)

So, the phase difference is f + π/2

Path Difference = (λ/2π)(f + π/2)

Hence, the correct option is b.

Two sources are said to be coherent if there always exists a constant phase difference between the waves emitted by these sources. But when the sources are coherent, then the resultant intensity of light at a point will remain constant and so interference fringes will remain stationary.

The necessary condition for phenomenon of interference to occur are:
1. There should be two coherent sources.
2. The frequency and amplitude of both the waves should be same.
3. The propagation of waves should be simultaneously and in same direction.
These are the conditions, no explanation.

A stationary charge doesn't produce a magnetic field , it only produces an electric field.

Earlier force between two particles is 
F=kq^1​q²​​/ r²
When distance is halved force becomes 
F′= kq₁​q²/(r/2)² ​​=4kq₁​q₂/r²​​=4F

We know that:
A capacitor consists of two plates of a conductor and a dielectric insulator between them:

Where
C = capacitance in farad
ϵ = Permittivity of dielectric
A = area of plate overlap in square meters
d = distance between plates in meters
If the area of the plates is halved i.e., A/2 and the distance between them is halved i.e., d/2, then new capacitance is:

Equipotential surfaces are surfaces in space where the electric potential is the same at every point. In other words, if you place a charge on an equipotential surface, it will not experience any force due to the electric field created by other charges in the system.

Now, consider a point on an equipotential surface. If the electric field at this point were not perpendicular to the surface, there would be a component of the electric field along the surface. This would mean that there is a potential difference along the surface, which contradicts the definition of an equipotential surface (where the potential is constant along the surface).

Therefore, for any charge configuration, the electric field at a point on an equipotential surface must be perpendicular to the surface. This can be understood intuitively by imagining that if there were a component of the electric field along the surface, charges on the surface would move to regions of higher or lower potential, violating the condition of an equipotential surface

BC and AC are in series

Now BA and DC are in parallel.

According to recent researches the magnetic field of earth is considered due to a large bar magnet situated in earth's core.
It is considered that the north pole of this large magnet is situated at the geographical south of earth and vice versa and as the magnetic field due to a bar magnet is from north pole to south pole of the maget thus the earth's magnetic field is considered from geographical south to geographical north which are respectively north and south poles of the bar magnet.

The earth's magnetic field is Be​ and its horizontal and vertical components are H_e​ and H_v​
cosθ= H_e​​/B_e​
∴cos60^o= (​0.26×10^−4​/ B_e )T
⇒B_e​=(​0.26×10⁻⁴)/ (½)​=0.52×10⁻⁴T=0.52G

Explanation:for electromagnetic induction magnet and coil both may move but relative motion between must be present

• The iron core of a transformer is made of Laminated silicon steel with special insulated coating to limit Eddy current loss.
• Electrical steel, also called lamination steel is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area (small energy dissipation per cycle, or low core loss) and high permeability.
  

Resonance occurs when X_L = X_C and the imaginary part of the transfer function is zero. At resonance the impedance of the circuit is equal to the resistance value as Z = R.

Hotwire instruments are based on the heat I_rms²​Rt and/or power I_rms²​R producing property of current. Hence it can measure both ac and dc current as both produce heat when passed through a conductor.

Light from each point on a luminous object travels outward in all directions in straight lines. Light travels at very high speeds, but is not instantaneously everywhere. Light from a point object travels indefinitely until it collides with matter in its path to be partially absorbed and reflected.

P=P1​+P2​=+2−1=+1 dioptre, lens behaves as convergent
F=1​/P=1/1​=1m=100cm

More than 99.99% of the mass of any atom is concentrated in its nucleus. If the mass of protons and neutrons (which are in the nucleus of every atom) is approximately one atomic mass unit, then the relative mass of an electron is 0.0005 atomic mass units.