Longitudinal and Transverse Waves

 LONGITUDINAL WAVES

The waves in which the particles of a medium vibrate in the  direction of propagation of wave are called a longitudinal wave.

These waves propagate in the form of compressions and rarefactions.

Example: Sound waves in air.

TRANSVERSE WAVES

The waves in which the particles particles of a medium vibrate in the direction perpendicular to the direction of propagation of waves are called transverse waves.

These waves propagate in the form of Crests and troughs 

Example: water ripples

PRESSURE COOKING

 QUESTION 

Why is food cooked quickly in a pressure cooker ?

Boiling:

 The process in which a liquid changes into gaseous state at a constant temperature and pressure is called boiling. 

Example: water boils at 100°C to change into steam.

Boiling  point:

The temperature at which boiling takes place at a given pressure is called boiling point. 

Example: The boiling point of water is 100°C. 

Boiling of  a liquid starts when the vapour pressure of the liquid heated is equal to the air pressure above the liquid surface. If we can increase the pressure above the liquid surface then boiling is  delayed and hence the boiling point is increased. 

So, when steam is retained inside the cooker, boiling point of the liquid increases to 120-125°C.

As the food is cooked at higher temperature in the pressure vessel, it is cooked easily and quickly.

PRISM and ANGLE OF PRISM

 PRISM

Prism is a transparent retracting medium bounded by at least two plane surfaces inclined at a certain angle.

ANGLE OF PRISM

The angle between two retracting surfaces of a prism is called angle of prism.

ANGLE OF DEVIATION

The angle between the direction of incident ray and the emergent ray is called angle of deviation. 

The angle of deviation depends on

1. Angle of incidence. 

With the increase in the angle of incidence , the angle of deviation first decreases ,then reach a minimum value then it also increases.

2.Refractive index of the material of the prism.

With the increase in the refractive index angle of deviation increases.

3. Colour o wavelength  of light 

With the increase in wavelength of light used, the angle of deviation decreases . Red is deviated the least and violet the most. 

4. Angle of prism or thickness of the prism 

The angle of deviation increases with increase in the  the angle of  de prism.

PASCAL'S LAW

 PASCAL'S LAW:

The pressure exerted at any point in a confined liquid is transmitted equally and undiminished in all direction throughout the liquid.

Pressure at a point in a liquid =F/A, Pressure at any other point in the liquid=F'/A'

As pressure is transmitted equally,   F/A=F'/A'

Applications

1.Hydraulic press.

2. Hydraulic lift.

3.  Hydraulic brakes.

CRITICAL ANGLE FOR DIFFERENT COLOURS OF LIGHT

 CRITICAL ANGLE:

The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90°.

FACTORS:

The critical angle of a medium depends on

1. The relative refractive index of the denser medium with respect to the rarer medium. Greater the refractive index, smaller the critical angle. 

For example: refractive index of glass is 1.5, critical angle is 42° and for diamond, refractive index is 2.4, the critical angle is 24°

2. The colour(wavelength) of the light. Longer the wavelength, greater  is the the value of the critical angle.

For example:  Red has longest wavelength among seven colours, so it has maximum value of the critical angle for a medium.

Atmospheric pressure

 What is atmospheric pressure?

Answer: The force exerted per unit area on the surface of the earth due to the weight of air  column above it is called atmoshpheric pressure.

Its SI unit is N/m² or pascal. Other units are dyne/cm², mm of mercury, bar, torr,

Unstable Hydrogen isotope can not emit alpha rays. Why?

 QUESTION: Unstable hydrogen can not emit alpha particles Why ?

Unstable hydrogen, though radioactive, can not emit alpha rays because during alpha decay two protons and two neutrons are emitted which are not present in the hydrogen atom. Hydrogen  has only one proton in its nucleus.

EARTHEN POT: An earthen pot keeps water cool..

 QUESTION: An earthen pot keeps water cool. How ?

Answer: The earthen pot has fine pores through which water comes out to the outer surface where evaporation takes place. During evaporation, the liquid absorbs heat from the surrounding keeping it cool.

g and G, The differences. Class 9

 

The acceleration due to gravity (g) 

1. It is the acceleration caused by the gravitational force.

2. Its value depends on the mass and radius of a planet or heavenly body.

3. Its value changes from place to place.

4.Its a vector quantity.

The universal gravitational constant(G)

1. It is numerically equal to the force of attraction between two bodies each of mass 1kg separated by distace of 1m.

2. Its value does not depend on the mass and size of bodies. 

3. Its value is constant everywhere in the universe. 

4. It's a scalar constan.

3. 

NEW SIGN CONVENTION OF CONVEX AND CONCAVE LENS.

 New sign convention for convex and concave lenses. 

1. The optical centre of the lens matches with the origin of  two dimensional cartesian system ( the point of intersection of x-axis and y-axis).

2. The object should be placed at the left side of the lens( towards negative x-axis).

3. The distances are measured from the optical centre of the lens( the origin). Assign the signs according to the signs of the segments of the axes.(x or y axis).

For CONVEX LENS.

4. The  object distance (u) is always negative.

5. The image distance (v) is positive for real images.

6. The image distance (v) is negative for virtual image.

7. The focal length (f) is positive. (Second local length)

For CONCAVE LENS.

8. The object distance (u) is always negative.

9. The image distance (v) is always negative as it forms virtual image.

10. The focal length (f) negative. (Second local length)

For OBJECT and IMAGE  lengths.

11. The length of the image is positive as it is always kept erect.

12. The length of the real image is negative  as it is inverted.

13. The length of the virtual image is positive. 

For MAGNIFICATION, (m=Image  length÷ object  length)

14. m is negative for real images.

15. m is positive for virtual image.

For NUMERICALS,

16.  Do not assign  any sign for unknown quantities. 

LENS FORMULA 

17.  Magnification (m)= Size of the image÷size of the object.

18. m= image distance  ÷object distance.

19.  Lens formula: 1/f= 1/v-1/u.

DOES CONVEX LENS FORM VIRTUAL IMAGES?

Question: Does convex lens form virtual images?

Answers: Yes, convex lens can form virtual image when the object is placed at the position between the first focus and the optical centre of the lens. The image is upright and magnified. Its formed on the same side of the lens where object is placed.

REVISION QUESTIONS ON KINETIC THEORY OF MATTER CLASS 8

 PHYSICS, CLASS 8

ALL QUESTIONS ARE COMPULSORY.

Q1. WHY DO WE SMELL HOT FOOD FROM A DISTANCE? 2

Q2. WHY IS THERE NO CHANGE IN TEMPERATURE DURING THE MELTING  PROCESS? 2

Q3. DIFFERENTIATE BETWEEN BOILING AND EVAPORATION WITH 3POINTS. 3

Q4. STATE AND EXPLAIN ANY THREE POSTULATES OF KINETIC THEORY. 3

Q5. DEFINE TWO TYPES OF INTERMOLECULAR FORCE WITH ONE EXAMPLE OF EACH. 2

Q6 EXPLAIN THE PROCESS OF MELTING ON THE BASIS OF KINETIC THEORY OF MATTER. 2

Q7. EVAPORATION CAUSES COOLING . GIVE REASON WITH ONE EXAMPLE. 2

Q8. WHY DOES A CAMPHOR GET CONVERTED TO FUMES ON HEATING? 2

Q9. WATER ______________HEAT DURING FREEZING AND _________ HEAT DURING BOILING. FILL IN THE BLANK WITH “ GAINS OR LOSES" 2

......*************......

Answers: 

A1. The molecules of food in gaseous form are free to move in  large intermolecular space available between them and the air and these molecules show zigzag motion  to different parts of a house. So, we can smell hot food from a distance.

A2. During melting process, the heat given to a solid is utilized to do work against intermolecular force of attraction. The heat energy changes completely into potential energy. Hence temperature does not change.

A3.                   Boiling                                                        I                   Evaporation

a) Boiling is a fast process.                                    I        a) Evaporation is a slow process.

b) Boiling does not  cause cooling                        l       b) Evaporation causes cooling.

c) Boiling takes place at a particular                    I      c) Evaporation takes place at any temperature. 

Temperature 

A4. I) Matter is made of atom or molecule..

Matter is made of small particles called atoms or molecules which cant be seen by naked eyes

ii) The molecules are always inconstant, random motion.

The particles continuously move in a zigzag path .

iii) The molecules possess kintic and potential energy.

Due to their motion the molecules possess kinetic energy. As they interact with other molecules, they change their position and possess potential energy.

A5. I) Force of cohesion : The force of attraction that exists between similar kinds of molecules.  Example: The force of attraction between molecules of water. 

ii) Force of adhesion: The force of attraction that exists between molecules of different substances. Example: The wetting of glass due to the force of adhesion between the molecules of water and glass. 

A6.  When a solid is heated,  the molecules gain kinetic energy and start overcoming the strong intermolecular force of attraction. At a particular temperature, the molecules completely overcome the force of attraction and the molecules becomes free to flow and the solid changes  into liquid . This process is called melting. 

A7. Evaporation causes cooling because the liquid absorbs heat from the body and the surrounding to evaporate. Earthen pot keeps water cool by evaporation of water from the surface of the pot.

A8. Camphor molecules have very weak intermolecular force of attraction. By absorbing  heat from surrounding these molecules overcome the force easily and molecules becomes free like gaseous molecules. Hence it is directly converted to fumes.

A9. Loses, gains.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%^^

REVISION QUESTIONS ON MEASUREMENT CLASS 7

CLASS 7 PHYSICS 

FULL MARKS :20

All questions are compulsory.

Q1. Write the full form of FPS, CGS and MKS system of unit. 3

Q2. State the SI unit of i)  Luminous intensity ii) Temperature iii) Electric current . 3

Q3 A block of mass 1000 kg has volume 2 metre cube. Calculate its density in i) kg/ metre cube   ii) g/cm cube. 3

Q4. A bus covers 200km in 5 hr and a car covers 105 km in 3hr. Which of the two travels faster? 3

Q5. Define density and state its SI unit. 2

Q6. Give reason : The density of iron is more than that of cotton. 2

Q7.  Name two devices to measure the volume of an object. 2

Q8. The space occupied by a solid is called ___________ and the amount of surface of a body is called ______________.  2

Answers:

A1. FPS: Foot, Pound,  Second .  CGS: Centimetre, gram, second.  MKS: Metre, kilogram,  Second.

A2. I) candela   ii) kelvin   iii) ampere

A3.  m =1000kg,  V=2 metre cube.  Density =m/V=1000/2= 500kg /m cube.  Density= 500/1000 g/cm cube.=0.5 g/cm cube.

A4. For the bus, distance= 200km, time= 5hr. Speed of the car=distance/time=200/5=40km/hr. 

       For the car, distance=105km, time= 3hr.  Speed of the car=distance/time= 105/3=35 km/h 

       Hence, the bus is faster.

A5. Density is defined as mass per unit volume of a body. Its SI unit is kg/m cube.

A6. The density of iron is more than that of cotton because the molecules are more closely packed in  iron than in cotton. 

A7. Measuring cylinder and measuring beaker.

A8. Volume, area.

::::::::::::::::::::::::::::::::::::::;;;;;:::::::::::%%%%%%%%%%%%%%%%%::::::::::::::::::::::::::::::::::;;;;;;;;::::::::::::

REVISION QUESTIONS , CHAPTER 1, CLASS 9, MEASUREMENT

CLASS 9, PHYSICS

FULL MARKS : 20

All Questions are compulsory. 

Q1. Define : a) measurement,  b) unit of a physical quantity.  2

Q2. State the SI unit of a) Luminous intensity,  b) solid angle. 2

Q3. Fill in the blanks a) 1 metre= _____________ micrometre.

                                      b) 1 Kg= _____________ metric tonne. 2

Q4. Compare the time period of two pendulum of length 2 m and 18 m. ( g=9.8 metre per square second) 2

Q5. State how does the time period of a simple pendulum depends on a) acceleration due to gravity, 

        b) length of pendulum and   c) amplitude of oscillation. 3

Q6. Define a) amplitude of a simple pendulum, b) frequency  of a simple pendulum  and c) seconds pendulum. 3

Q7. What are the three requirements  for selecting a good unit of a physical quantity. 3

Q8 Write the derived unit of FORCE ( in terms of symbols of basic units) in a) MKS b) CGS and c) FPS system of unit. 3

ANSWERS:

A1. a) Measurement is the process of comparing the value of a physical quantity with a chosen standard value of same kind. B) The standard quantity selected to measure a physical quantity is called  a unit.

A2a) candelabra   b) steradian

A3 a) 10^6 ( ten to the power of six) b) 10^-3

A4. T1/T2=\ /~~l1/l2 =\/~2/18=\/~~1/9=1/3= 1:3

A5. Time period is inversely proportional to the square root of acceleration due to gravity. 

Time period is directly proportional to the square root of the length of a pendulum.

Time period does not depend on the amplitude.

Answers from 6 to 8 for your practise (Please do it yourself ) If you want any answers please do write in comment section.

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::%%%%%%%%%%%%:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

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. 

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

 $$$$$$$$$$$$$$$$$$$$$$sharmadiwakar$$$$$$$$$$$$$$$$$$$$$$ 

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.

COMMERCIAL UNIT OF ENERGY

The commercial unit of electric energy is kilowatt hour. We have 

Energy =power ×time. Accordingly, Killowatt hour is the commercial unit as this unit is used to  measure electric energy and to prepare electricity bill.

What is Electroscope?

It is a device to detect and to identify electric charge. Examples of electroscope: Pith Ball and Gold leaf electroscope.

Why is loud sound heard during the process of Resonance?

Loudness depends on the amplitude of sound wave . In resonance, amplitude increases when natural frequency matches with the frequency of external force. As amplitude increases, loudness of the sound increases.

FOCUS OF A CONCAVE MIRROR

Focus is a point on the principal axis where the incident rays parallel to the principal axis meet after reflection. Highly diminished image is formed at focus if the object is
placed at infinity.

When does a nucleus become unstable?

A nucleus becomes unstable when number of neutrons in the nucleus is  more than the number of protons

Why is handle fitted near the edge of a door?

The moment of force directly proportional to the force and perpendicular distance of force from the axis of rotation. For a given moment of force, smaller force is required if it is applied at a longer distace from the axis of rotation. To open the door with least force ,handle is fitted near its edge.