NEET Practice Test - 18 - NEET MCQ

• The electrons in the base are called minority carriers because the base is doped p-type, which makes holes the majority carrier in the base.
• In an npn transistor, the majority charge carriers in base is holes and minority charge carriers are electrons.

NPN Transistor:

Considering each edge length be 'a'.
Then, volume of cube = a³
Also, surface area of the same cube = 6a²
According to the question, both of them are equal.
i.e., ►  a³ = 6a²
This brings us to the conclusion, a = 6m.
Thus, volume of cube is 216 m³.

► The acceleration of the ball will be g.
     Initial velocity will be 0. 
     In T sec body travels h metres.  

► By applying equations of motion we get

► from (1) and (2) we get h₁ ​= h/9 distance from point of release.

∴ Distance from the ground is: 

In a uniform circular motion, acceleration is always towards center and velocity is along the tangent. So, θ=90^∘.

Body A has acceleration a.
Let acceleration of B be b.
► Mb = F – T
where T = Ma
► Mb = F – Ma
► b = {(F – Ma) / M}
b = [(F / M) – a] 

According to Newton's second Law,
► T₁ = m₁ a
► T₂ = (m₁ + m₂)a
► (T₁ / T₂) = {m₁ / (m₁ + m₂)}
= {3 / (3 + 12)} = (1 / 5)

Hence, T₁ : T₂ = 1:5  

For the equilibrium of block of mass M: 
Frictional force, f = tension in the string, T
where T = f = µ(m + M₁)g   ...(i)
For the equilibrium of block of mass M:
► T = M₂g     ...(ii)
From Eqs. (i) and (ii), we get μ(m + M₁)g = M₂g
► m = M₂/μ - M₁

• According to the law of conservation of linear momentum when two bodies of same mass collide they exchange velocities.
• ∴ Only two marbles from the extreme right will roll with a speed 'V' and the other balls will remain at rest.

Given:
Power = 2kw = 2000w 
Height H = 10m 
Time taken t = 60 seconds
Now,
► Power = Energy/time = mgh / t
2000 = m*10*10 / 60
We get m = 1200 kg
Therefore, the pump lifts 1200 kg or 1200 litres of water to a height of 10m every minute.

Kinetic energy is:
K = (1/2) mv²
We want to write it in form of momentum. We know that momentum, P = mv
Multiply and divide by m,
► K = (1/2) m² v² / m
► K = (1/2) (mv)² / m
► K = (P²) / 2m
Thus Kinetic Energy is proportional to the square of momentum.
Also, P = √(2mK)
So, momentum is proportional to the square root of kinetic energy.
Thus, if kinetic energy is doubled, then momentum will become √2 times the original momentum.

Centripetal force = mv²/r
Angular momentum = mvr = L
Thus centripital force,

According to the law of conservation of energy, as no non-conservative external or internal force acts upon the system, energy is conserved, thus we have,
mgh = ½ I w² 
where I is moment of inertia and w is angular speed.
I = mL² / 3 and w = v / L
Thus we get, 
► mgL = mv² / 3
Thus we get v = √3gL
Thus we get v = 5.4m/s

∴  we have

► R + h = 10 R  
► h = 9R, which is option B.

From Hooke's law, if the strain is small then stress is proportional to strain, i.e.,
stress = Y×strain
where Y is a proportionality constant called Young's modulus.
Young's modulus is given by:


where F is force, A is area.
Δl is change in length and L is original length. First case,
  ... (i)
Second case,
  ... (ii)   
Equating Eqs. (i) and (ii), we get:

                   

From the equation of terminal velocity we have
 
Here we see that: 

Excess pressure(P) in first drop = 1.01 - 1 = 0.01 atm
Excess pressure in second drop = 1.02 - 1 = 0.02 atm

Pressure × Radius = Surface Tension
Here the pressure is Gauge Pressure, i.e the difference between absolute pressure and atmospheric pressure
Hence ratio of gauge pressures is 1:2
Accordingly ratio of radii is 2:1 
Since Volume ∝ (Radius)³
Hence ratio of volumes is 8:1
P is inversely proportional to r(radius). So ratio of their volumes will be:
► r₂³ / r₁³ = (0.02)³ / (0.01)³ = 8 : 1

• Density of water is maximum at 4°C and density will decrease if we cool it above 4°C or heat above 4°C.
• So for mass to remain constant, the volume should increase and when volume increases, water overflows.

We know, 
[∵ The wires A and B are pulled by the same force and they are made up of same material hence, F_A = F_B = F, Y_A = Y_B = Y]

First law in Adiabatic Process:
► ΔQ = ΔU + ΔW
Since, ΔQ = 0 (in Adiabatic Process)
► ΔU + ΔW = 0
► ΔU = ΔQ - W
► ΔQ = 2 K cal = 2 x 4.2 x 1000 J = 8400 J
► W = 500 J
∴ ΔU = (8400 - 500) J = 7900 J

If pressure and volume of gas remains constant then MT = constant 

According to first law of thermodynamics,
ΔQ = ΔU + PΔV 
If ΔQ is absorbed at constant volume, ΔV = 0

for an ideal monoatomic gas

Acceleration =−w²y.
So, F = - mw²y is sinusoidal function.
So, F will be also a sinusoidal function with phase difference p.

Given , y = 4sin(πx / 15) cos 96 πt
For nodes, displacement is zero.
∴ sin(πx/15) ​= 0
⇒ πx / 15​ = 0, π, 2π...
⇒x = 0, 15, 30...
For antinodes, displacement is maximum.
∴ sin(πx/15) ​= 1
⇒ (πx/15)​ = 2π​, 23π​...
⇒ x = 15/2​, 45/2​
Hence the difference between node and antinode = 15/2 ​− 0 ​= 7.5 m

As we know according to the Doppler effect the speed of the listener and source are the same so both of them heard the same frequency.

i.e., net charge on dipole is zero. 

The two condensers in the circuit are in parallel order, hence:
► C' = C + (C/2) = 3C/2

The work done in charging the equivalent capacitor is stored in the form of potential energy.
► W = U = C'V² / 2
= 3CV² / 4

The equivalent circuit may be shown as:

Where R may be treated as the total resistance.