Physics - Online Test
Q1. A piece of copper and another of germanium are cooled from room temperature to 80K. The resistance
Answer : Option B
Explaination / Solution:
Copper is a conductor and we know that for conductors, resistance is directly proprtional to temperature. Therefore on decreasing temperature resistance also decreases.
Whereas, germanium is a semiconductor and for semiconductors, resistance is inversely proportional to temperature. So on decreasing temperature resistance increases.
Q2.
A beam of alpha particles is incident on a target of lead. A particular alpha particle comes in “head-on” to a particular lead nucleus and stops 6.5 m away from the center of the nucleus. (This point is well outside the nucleus.) Assume that the lead nucleus, which has 82 protons, remains at rest. The mass of the alpha particle is 6.64 kg What initial kinetic energy (in MeV) did the alpha particle have?
Answer : Option D
Explaination / Solution:
No Explaination.
Q3. A parallel combination of 0.1 MΩ resistor and a 10 μF capacitor is connected across a 1.5 V source of negligible resistance. The time (in seconds) required for the capacitor to get charged up to 0.75 V is approximately
Answer : Option A
Explaination / Solution:
A capacitor is charged when the resistance is connected in series with the capacitor. The time constant of the circuit . The capacitor will not be charged.
Q4. A particle is orbiting in a vertical plane. Its linear momentum will be directed
Answer : Option D
Explaination / Solution:
As the direction of velocity at any point moving in circular orbit is tangent at that point, thus momentum would be tangential to the orbit.
Q5. Two match sticks are laid side by side on the surface of water. When a drop of light oil on the end of a third match stick is touched to the surface film between the two floating sticks, the two match sticks
Answer : Option D
Explaination / Solution:
No Explaination.
Q6. for motion under an external conservative force
Answer : Option D
Explaination / Solution:
Mechanical energy is the sum of the potential and kinetic energies in a system. The principle of the conservation of mechanical energy states that the total mechanical energy in a system (i.e., the sum of the potential and kinetic energies) remains constant as long as the only forces acting are conservative forces.
Q7. A house has well-insulated walls. It contains a volume of 100 of air at 300 K. Calculate the energy required to increase the temperature of this air by 1.00C.
Answer : Option A
Explaination / Solution:
Q=nCPΔT=72RnΔT=72(PVT)ΔTQ=72×(1.01×105×100300)×1=118KJ
Q8. A lamp and a screen are set up 100 cm apart and a convex lens is placed between them. The two positions of the lens forming real images on the screen are 40 cm apart. What is the focal length of the lens ?
Answer : Option B
Explaination / Solution:
No Explaination.
Q9.
90 of a radioactive sample is left undisintegrated after time τ has elapsed, what percentage of initial sample will decay in a total time?
Answer : Option B
Explaination / Solution:
No Explaination.
Q10. A student eats a dinner rated at 2000 Calories. He wishes to do an equivalent amount of work in the gymnasium by lifting a 50.0-kg barbell. How many times must he raise the barbell to expend this much energy? Assume that he raises the barbell 2.00 m each time he lifts it and that he regains no energy when he drops the barbell to the floor.
Answer : Option D
Explaination / Solution:
Total no.of times he lift barbell = Total energy / energy in lifting barbell once
