Physics - Online Test

Q1. If an electron accelerated through a potential difference of 500 volt attains a speed of 1.33  then specific charge of the electron should be
Answer : Option B
Explaination / Solution:

eV0=12mv2em=v22V0=(1.33×107)22×500=1.76×1011CKg1
Q2. To increase the range of line of sight communication
Answer : Option B
Explaination / Solution:
No Explaination.


Q3. A cricketer hits a cricket ball from the ground so that it goes directly upwards. If the ball takes, 10 s to return to the ground, determine its maximum height.
Answer : Option D
Explaination / Solution:

We know that at the maximum height, the velocity of the ball is 0 m/s.

We also know that the ball takes the same time to reach its maximum height as it takes to travel from its maximum height to the initial position, due to time symmetry. The time taken is half the total time.

Therefore, we have the following information for the second (downward) part of the motion of the ball:

t = 5 second; half the total time


g = 9.8 m/s​​​​​​2 downward

s = ?

As we know

s = ut+

Put all the given value,

=> s = 

=> s = 122.5 m

 


Q4. Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is . (a) What is the net charge inside the box? (b) If the net outward flux through the surface of the box were zero, could you conclude that there were no charges inside the box? 
Answer : Option C
Explaination / Solution:

(a) Net outward flux through the surface of the box, ϕ = 8.0 ×  N /C For a body containing net charge q, flux is given by the relation,  = Permittivity of free space = 8.854 ×  N^{−1} We have q = ϕ = 8.854 ×  × 8.0 ×  = 7.08 ×  = 0.07 μC Therefore, the net charge inside the box is 0.07 μC. (b) No Net flux piercing out through a body depends on the net charge contained in the body. If net flux is zero, then it can be inferred that net charge inside the body is zero. The body may have equal amount of positive and negative charges.

Q5. A copper cube measures 6.00 cm on each side. The bottom face is held in place by very strong glue to a flat horizontal surface, while a horizontal force F is applied to the upper face parallel to one of the edges. How large must F be to cause the cube to deform by 0.250 mm? (shear modulus of copper = 4.4   Pa)
Answer : Option A
Explaination / Solution:
No Explaination.


Q6.

A 1.0-kg bar of copper is heated at atmospheric pressure. If its temperature increases from 20C to 50C, what is the work done by the copper on the surrounding atmosphere? Given  that for Cu = 5.1  x 10-5 / C, 


Answer : Option D
Explaination / Solution:

ΔV=3αViΔT=5.1×105×30×Vi=1.5×103ViΔV=1.5×103mρCu=1.5×10318.92×103=1.7×107W=PΔV=1.01×105×1.7×107=1.7×102J
Q7.

A man of mass 70 kg stands on a weighing scale in a lift which is moving upwards with a uniform speed of 10 m . What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?


Answer : Option B
Explaination / Solution:

When the lift falls freely under gravity, a=g

Therefore Apparent weight, 

This is the condition of weightlessness.


Q8. In the measurement of resistance by a metre bridge, the current is necessarily reversed through the bridge wire to eliminate
Answer : Option D
Explaination / Solution:

The connecting metal strips include a small resistance in the circuit called the end resistance. On reversing the current, the end resistance tends to get cancelled out.

Q9. A block having a mass of 0.80 kg is given an initial velocity 1.2 m/s to the right and collides with a spring of negligible mass and force constant k =50 N/m. Assuming the surface to be frictionless, calculate the maximum compression of the spring after the collision.
Answer : Option C
Explaination / Solution:

for maximum compression 


the maximum compression of the spring after the collision = 0.15m


Q10. Average angle of deflection of α -particles by a thin gold foil predicted by Thomson’s model is
Answer : Option C
Explaination / Solution:
No Explaination.