Waves — Physics STD 11 Science — Question

Three light sources A, B and C emit equal amount of radiant energy per unit time. The wavelengths emitted by the three sources are 450nm, 555nm and 700nm respectively. The brightness sensed by an eye for thesources are X_A, X_B and X_C respectively. Then, 

1. X_A > X_B, X_C > X_B
2. X_A > X_B, X_B > X_C
3. X_B > X_A, X_B > X_C
4. X_B > X_A, X_C > X_B

A cylindrical wooden block of cross-section 15.0cm² and mass 230gm is floated over water with an extra weight 50gm attached to its bottom. The cylinder floats vertically. From the state of equilibrium, it is slightly depressed and released. If the specific gravity of wood is 0.30 and g = 9.8m per sec², find the frequency of oscillation of the block.

When you come out of a river after a dip, you feel cold. Explain.

If all the objects radiate electromagnetic energy, why do not the objects around us in everyday life become colder and colder?

A mass m moving with a speed u collides on a similar stationary mass and sticks to it. What is the velocity after collision?

What is the relation between the coefficient of linear expansion and coefficient of volume expansion?

Write the definition of efficiency of a heat engine.

What is the average friction force when a person has a usual 1km walk?

Water flows at a speed of 6cm/s through a tube of radius 1cm. Coefficient of viscosity of water at room termperature is 0.01 poise. Calculate the Reynolds number. Is it a steady flow?

What is moment of inertia of a solid sphere about its diameter?