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. 

STONE AND WATER

Question:

Why does a stone lying in the sun get heated up much more than water lying for the same duration of time?

Answer:

The specific heat capacity of  stone is less than the that of  water.

ECHO IN LIVING ROOM

Why is echo not heard in our living rooms?

To hear echo, the minimum distance between the source and the reflector must be 17m. When this distance is more than 17m, the reflected sound can be distinguished from the original. As the length of our rooms is less than 17m, we don't hear echo.

SAMPLE PAPER FOR ICSE 2020 onwards, PHYSICS EXAM, 13 MARCH 2020

 SAMPLE PAPER FOR ICSE 2020 onwards, PHYSICS EXAM, 13 MARCH 2020 

PHYSICS
CLASS 10
FULL MARKS 80

GENERAL INSTRUCTIONS: 1. ANSWERS TO THIS QUESTION PAPER SHOULD BE WRITTEN IN ANSWER SHEETS PROVIDED SEPARATELY. 2. You ARE NOT ALLOWED TO WRITE IN FIRST 15 MINUTE. SPEND THIS TIME TO READ THE QUSETIONS THOROUGHLY. 3. THIS QUESTION PAPER IS DIVIDED INTO TWO SECTIONS: SECTIONS A AMD SECTION B. 4. SECTION A: ATTEMPT ALL QUESTIONS FROM THIS SECTION. 5. SECTION B : ATTEMPT ANY FOUR QUESTION. 6. MARKS ARE GIVEN IN BRACKETS [ ].

 SECTION A (ATTEMPT ALL QUESTIONS )

 QUESTION 1

 a) Define centre of gravity and mark it for a triangular lamina. 2
 b) A body of mass 500g is thrown vertically upwards with a velocity of 9.8 m/s, calculate the potential energy at the maximum height. (g=10m/s^2) 2
c) Name the class of lever for a short handle oar. Give one more example of this class of lever. 2
 d) Screw Jack has a long handle bar. Give reason. 2
e) A force displaces an object but does no work. Give two examples. 2

QUESTION 2

a) Draw a diagram to show how a right isosceles prism behave in a binocular. 2
b) State two laws of refraction. 2
 c) A lens forms virtual and magnified image. Draw the ray diagram for the same. 2
d) Name the waves used in echo ranging method of SONAR. Why are these waves used? 2
e) Smoke appears white. Give reason. 2

 QUESTION 3

a) An enemy plane is at a distance of 600 km from a RADAR. A wave takes 0.004 s to come back from the plane to the RADAR. Find the speed of the wave and name it. 2
b) How is the frequency of stretched wire related to its tension and and its length. 2
 c) A solid of mass 100g at 100°C is placed in 100g of water at 10°C,when the final temperature is 30°C. Find the specific heat capacity of solid. Specific heat capacity of water is 4.2J/(g°C). 2
 d) Two bulbs A and B are rated 100W,120V and 10W, 120 V respectively. They are connected in parallel across a 120V source. Calculate the current in first bulb and explain which bulb will consume more power. 2
e) Draw a labelled diagram of d.c.motor. 2

 QUESTION 4

 a) Find the equivalent resistance of the resistors. 2
 b) State the principle of calorimetry. 2
 c) When does a nucleus of an atom tends to be radioactive? 2
d) Define nuclear fusion. Give one example with nuclear reaction. 2
e) Why is fuse connected in live wire? 2

SECTION B
(ATTEMPT ANY FOUR QUESTIONS)

QUESTION 5

 a) Two bodies travel with uniform velocities 3u and 5u to have kinetic energy in the ratio 81:75. Find the ratio of their masses. 2
b) A pump is used to lift 500kg of water from a depth of 80 m in 10s Calculate the i) work done by the pump ii) the power rating of the pump it is 40% efficient. 2
c) State two methods to increase the efficiency of a block and tackle system 2
d) State the energy transformation in i) Photosynthesis in leaves ii) Charging a battery 2
e) Give one example of class 1 lever which acts as a force multiplier. Draw a labelled diagram. 2

 QUESTION 6
 a) Rohan claims to have obtained an image twice the size of the object with a concave lens. Is he correct? Give a reason for your answer. 2
b) Draw a ray diagram Of refraction of light through a medium where incident ray is parallel to emergent ray. 2
c) State two conditions required for the occurrence of total internal reflection 2
 d) How does the value of angle of deviation produced by a prism changes with the increase in the value of the angle of incidence and the wavelength of incident light. 2
e) Name the radiations that are used in sending signals during war. Give reason for your selection.2

 QUESTION 7

 a) A vibrating tuning fork is placed over the mouth of a burette filled with water.The tap is opened and the water level gradually falls. It is observed that the sound becomes the loudest for a particular length of air column. i) Name and define the phenomenon taking place. ii) Why does the sound becomes the loudest? iii) State one application of this observation. 4
 b) In the following circuit diagram, calculate i) The potential difference across 12 ohm resistor. ii) The energy dissipated in 8 ohm resistor in 15 seconds. 3
 c) State three differences betwern step up and step down transformers. 3

QUESTION 8
 a) Why is alternating current preferred over direct current for the long distance electric power transmission? Also give reason for the use of high voltage for such transmission 3
 b) Explain the meaning of the following statement: The specific latent heat of fusion of ice is 336000 J/kg. 2
 c) Calculate the amount of ice which is needed to cool 150g of water contained in a vessel of mass 100g at 30°C, such that the final temperature of the mixture is 5°C. The specific heat capacity of vessel is 0.4J/(g°C), [ Specific latent heat of fusion of ice=336J/g and specific heat capacity of water =4.2J/(g°C ] 3
d) A current carrying wire is placed in a magnetic field but experiences no force. Is it possible? Give reason. 2

QUESTION 9

 a) An element X changes to element Y by releasing 2 alpha particles and one beta particle. If there are 92 protons and 143 neutrons in the nucleus of X find the atomic number and no of neutrons of Y. 2
 b) Name two sources of Background Radiation. 2
 c) Mention two important precautions that should be taken while handling radioactive materials. 2
 d) Distinguish between Nuclear fission and fusion.3
 e) During the change of state of a substance, which, of Kinetic or Potential, energy changes in molecules? 1

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ELASTICITY

What is elasticity?

Elasticity is the property of a body by which the body regains it original configuration when the deforming force is released.

Elasticity doesn't  mean the force to stretch  a body or how much we can stretch a body.

SPEED OF SOUND IN WINTER NIGHT

Speed of sound decreases with the fall in temperature as density of medium increases due to cooling.

FOG REDUCES VISIBILITY, WHY?

Why does fog reduce visibility range?

The fog particles scatter  light of all colour to the same extent as the size of particles  of fog is same or greater than that of  wavelength of light. As colours are scattered, the fog appears white and on the other hand the light from the other side does not reach the observer, so it reduces visibility.

USES OF ULTRASOUND

ULTRASONIC WAVES

What are the properties of ultrasonic waves?

1 They carry large amount of energy with them as they have high
  frequency.
2. They travel in straight path.