Physics - Online Test
Q1. A pebble of mass 0.05 kg is thrown vertically upwards. Give the direction and magnitude of the net force on the pebble, if the pebble was thrown at an angle of 45° with the horizontal direction, Ignore air resistance
Answer : Option B
Explaination / Solution:
F = mg = 0.05 x 10 = 0.5 N. The horizontal component of the velocity remain constant.
Q2. Postulates are
Answer : Option D
Explaination / Solution:
A postulate is an assumption, that is, a proposition or statement, that is assumed to be true without any proof. Postulates are the fundamental propositions used to prove other statements known as theorems. Once a theorem has been proven it is may be used in the proof of other theorems.
Q3. The dielectric constant K of an insulator can be
Answer : Option D
Explaination / Solution:
Dielectric constant of air is 1. All dielectrics generally have a value of the dielectric constant greater than 1.where is the force between two charged particles in a medium of dielectric constant K and F is the force between the two charges when placed in air.The force between two charges is greatest in air or vacuum and it decreases when any medium is placed between the charges. K cannot have negative, fractional or zero values.
Q4. Angular momentum of a body is defined as the product of
Answer : Option A
Explaination / Solution:
if r is perpendicular to p (in case of circular motion)
L = mvr
Q5. If a film of width L is stretched in the longitudinal direction a distance d by force F, surface tension is given by
Answer : Option C
Explaination / Solution:
Let L be the width of the film. Since the film has two surfaces, the total length along which the surface force acts on the slider is 2L. The surface tension S in the film is defined as the ratio of the surface force F to the length d (perpendicular to the force) along which the force acts
S=F/d
Hence, in the case, d = 2L
S=F/2L
Q6.
Estimate the total number of air molecules (inclusive of oxygen, nitrogen, water vapor and other constituents) in a room of capacity 25.0 at a temperature of 27 C and 1 atm pressure.
Answer : Option D
Explaination / Solution:
PV=NkTN=PVkT=1.01×105×251.38×10−23×300=6.1×1026
Q7. A Plano convex lens of curvature of 30 cm & R.I. 1.5, produces a real image of an object kept 90cm from it. The magnification is
Answer : Option B
Explaination / Solution:
No Explaination.
Q8.
The particles or radiation emitted in the nuclear reaction will be respectively,
Answer : Option D
Explaination / Solution:
No Explaination.
Q9. If is the temperature of the surrounding medium and is the temperature of the body, then according to Newton’s Law of Cooling rate of cooling of the body is
Answer : Option B
Explaination / Solution:
Newton's law of cooling states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its surroundings.
Q10. A series LCR circuit with R = 20 , L = 1.5 H and C = 35 is connected to a variable-frequency 200 V ac supply. When the frequency of the supply equals the natural frequency of the circuit average power transferred to the circuit in one complete cycle is
Answer : Option D
Explaination / Solution:
When the frequency of the supply equals the natural frequency of the circuit
in this case impedance Z = R
average power
Pav=Vrms×irms×cosϕ=Vrms×VrmsZ×RZZ=RPav=(Vrms)2R=200×20020=2000W
