Physics - Online Test
Q1.
Give the magnitude and direction of the net force acting on a stone of mass 0.1 kg lying on the floor of a train which is accelerating with 1 m , the stone being at rest relative to the train. Neglect air resistance.
Answer : Option B
Explaination / Solution:
Weight of the stone is balanced by the reaction of the floor. The only acceleration is provided by the horizontal motion of the train.
a = 1ms-2
force in horizontal direction
F = ma = 0.1 x 1 = 0.1N
Q2. Technology is concerned with
Answer : Option A
Explaination / Solution:
Technology is the making, modification, usage, and knowledge of tools, machines, techniques, crafts, systems, and methods of organization, in order to solve a problem, improve a pre-existing solution to a problem, achieve a goal, handle an applied input/output relation or perform a specific function. It can also refer to the collection of such tools, including machinery, modifications, arrangements and procedures.
Q3. If the dielectric constant and dielectric strength be denoted by K and X respectively, then a material suitable for use as a dielectric in a capacitor must have
Answer : Option D
Explaination / Solution:
The capacitance of a capacitor increases with increase in the value of dielectric constant. =K C. Dielectric strength is the maximum electric field the material can withstand without breaking down. A high value of X and a high value of K is preferable for use in capacitors.
Q4. In an orbital motion, the angular momentum vector is
Answer : Option D
Explaination / Solution:
Hence direction of angular momentum is perpendicular to both and that is perpendicular to the orbital plane.
Q5. An iron needle floats on the surface of water. This phenomenon is attributed to
Answer : Option C
Explaination / Solution:
The answer lies in the surface tension of the water, As the cohesive forces between the molecules is responsible for the surface tension. When the molecules on the glass or container do not have a surface to stick to, they cohere more strongly to the molecules they are associated with. Since the molecules on top have no neighbours on the top to cohere to, they associate with their other neighbours more strongly. This creates a strong bond between the top layer of molecules. The molecules inward face no net force because they all cancel out each other. However, the surface molecules face a net inward force because there is no force for them on the surface to cancel it. This causes the molecules on the surface to 'contract' and resist being broken or stretched.
When a small body like a needle is placed onto the water carefully, the surface tension will not break due to the small mass of the object.
As long as the surface tension is undisturbed, the needle will continue to float. Agitating the water will cause the surface tension to break and hence the needle will then sink
As long as the surface tension is undisturbed, the needle will continue to float. Agitating the water will cause the surface tension to break and hence the needle will then sink
Q6. Estimate the average thermal energy of a helium atom at the temperature on the surface of the Sun (6000 K)
Answer : Option D
Explaination / Solution:
k = boltzman constant
Q7. When an astronomical telescope is focused on a distant star, the distance of the eye piece from the objective is 60 cm. When focused on a distant flag post the eye piece must be drawn at 0.1cm. If the focal length of the eye piece is 5cm; what will be the distance of the pole from the objective? Assume that the eye is focused for infinity?
Answer : Option B
Explaination / Solution:
No Explaination.
Q8. The half life of radium is about 1600 years. Of 100 g of radium existing now, 25 g will remain unchanged after
Answer : Option A
Explaination / Solution:
No Explaination.
Q9. The Celsius temperature at absolute zero is equal to
Answer : Option B
Explaination / Solution:
TC−0100−0=TK−273.15373.15−273.15
Q10. The magnetic field due to very long wire carrying current varies according to
Answer : Option C
Explaination / Solution:
The magnetic field at a point, which is at a distance r, from a very long wire carrying current is
