CRITICAL ANGLE

The angle of incidence of a ray in a denser medium for which the angle of refraction in rare medium is 90°, is called Critical angle for those pair of media. 

The critical angle depends on 

i) the density of medium.

ii) the colour of the light.

CONDITIONS FOR TOTAL INTERNAL REFLECTION. CLASS 10

1. The light ray should travel from denser to rarer medium.

2. The angle of incidence in the denser medium should be greater than the critical angle for the given pair of media. 

Total internal reflection (ICSE CLASS 10)

When a ray of light travels from denser to rarer medium at the angle of incidence greater than critical angle for the pair of media, the ray gets reflected back to the denser medium without any loss of energy. This phenomenon is called total INTERNAL reflection.

Characteristics of non contact forces. (ICSE CLASS 9)

The properties of non contact forces( gravitational,  electrostatic and magnetic forces) are as follows,

1. They are central forces. It means the non contact force acts along the line joining the centres of two bodies.

2. They follow inverse square law. It means a non contact force is inversely proportional to the square of the distance.

3. They can both be attractive and repulsive.

Atmospheric pressure and blood pressure

We don't feel the effect of enormous atmospheric pressure. Why?

We don't feel the effect because the pressure due to the blood and other fluids in our body balance it.

Efficiency of single movable pulley is always less than 100%. Give reason.

The efficiency is less than 100% because of the weight of the pulley and the friction in its axle.

Mechanical advantage of a block and tackle system increases on increasing the number of pulleys. Give reason

Mechanical advantage of the block and tackle system of pulleys increases because the number of strands balancing the load increases.

Red rose appears red in white light and black in green light. Why?

Red rose appears red in white light because it reflects red colour and absorbs all the other colours of white light, but appears black in green colour because the only colour given to the flower is absorbed and nothing is reflected.

TUNING FORK

QUESTION:

A vibrating tuning fork when held against the surface of a table produces a loud sound.  Give reason.

ANSWER:

A vibrating tuning fork forces the table top to vibrate. As the table top has large surface area, amplitude of vibration increases. 

2020 ICSE CLASS 10 PHYSICS QUESTION PAPER

Superconductors

QUESTION:

What are superconductors?

ANSWER:

The materials whose resistivity is zero at very low temperature is called superconductors. Example: Mercury below 4K.

Work done on satellite.

QUESTION:

A satellite revolves around a planet in a circular orbit. What is the work done by the satellite at any instant?

Answer:

The work done is zero.  As the Centripetal force by the satellite is perpendicular to the displacement of the body.

FUSE WIRE

QUESTION:

Why is it  not advisable to use a piece of copper wire as fuse wire in an electric circuit.?

ANSWER:

Fuse wire should have low melting point and high resistivity but copper has high melting point and low resistivity.