PHYSICS

 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

 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 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 : 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: 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.

 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,

 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.

 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.

  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 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...

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.

 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....

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=10...

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...

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.

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. 

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.

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.

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.

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

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 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.

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. 

QUESTION: What are superconductors? ANSWER: The materials whose resistivity is zero at very low temperature is called superconductors. Example: Mercury below 4K.

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.

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. 

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.

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  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...

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

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.

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.

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.

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 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.

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

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 op en the door with least force ,handle is fitted near its edge.