LOUD SOUND IS HEARD DURING RESONANCE

 QUESTION: Why is loud sound heard at RESONANCE?

 ANSWER: Loud sound is heard at RESONANCE because  amplitude increases when external  frequency is equal or integral multiple of the natural frequency of vibrating body.

EFFECTIVE COOLANT - WATER

Water has high specific heat capacity 4200J/(Kg°C) so it can absorb large amount of heat without much rise in it's own temperature.

ISLANDS ENJOY MODERATE CLIMATE

 Islands or coastal areas enjoy moderate climate. Why?

Ans. Water has higher heat specific capacity than the land due to which there is the continuous formation of sea breeze and land breeze near the coastal areas. This keeps the temperature moderate.

PRINCIPLE OF CALORIMETRY

If no heat is exchanged with surrounding, heat lost by the hot body is equal to heat gained by the cold body. 

70 to 80% water in plants and animals. Why?

Plants and animals have 70-80% water so that they can maintain body temperature as water has high specific heat capacity.

FARMERS FILL THEIR FIELDS WITH WATER.

Farmers fill their crop fields with water to protect from frost: why?

Water has high specific heat capacity so it delays the surrounding temperature to fall to zero degree Celsius ,thus protecting the crops from frost

FOMENTATION

Why is water used in fomentation ?

Water has high specific capacity due to which it cools slowly and imparts large amount of heat to our body.

ICSE ISC SEM 1 NOV 2021 EXAMINATION POSTPONED

ICSE and ISC semester 1 exams to be held in November 2021 is postponed. New datesheet will be released later.  It is now assumed that exam will be in offline mode.

REVISION QUESTIONS CLASS 10

PHYSICS REVISION TEST

CLASS 10 , MACHINESS AND REFRACTION OF LIGHT

ATTEMPT ALL QUESTIONS. 

Q1. Give two reasons for a  single movable pulley not to be 100% efficient. 2

Q2. What is the purpose of a Jack in lifting a car by it ? 2

Q3. Stars twinkle in the sky . Give reason.  2

Q4. Draw a labelled diagram of a block and tackle system with velocity ratio 5.     2

Q5 Name the single pulley with mechanical advantage more than one. State  its one disadvantage.2

Q6. State two laws of refraction 2

Q7 State two factors affecting refractive index of a medium. State the effect also.2

Q8. Which colour out of green and orange , is deviated the most. Give reason for your answer. 2

Q9. A water pond appears 1.35 m deep. If the refractive index of water is 4/3, find the actual depth of the pond. 2

Q10. What is total INTERNAL reflection?  2

Q11.Draw a diagram for the deviation of a light ray by 90°. 2

Q12 Which colour of the visible light has maximum critical angle.? Why? 2

Q13Explain the cause for sparkling of  a diamond. 2

Q14. Statr the principle of a simple machine. From which law is it derived? 2

Q15. State the principle of machines. 2

REVISION QUESTIONS, CHAPTERS 1& 2, CLASS 9 PHYSICS

 CLASS 9 Physics  

Q1 Name any two basic quantities and write their SI units.

 Q2.Name any two derived quantities and write their SI units.

Q3 What are the three requirements for selecting a unit of a physical quantity.? 

Q4. Define “light year". 

Q5. Compare the time periods of two pendulum of length 4m and 25 m.  

Q6. State two factors affecting the time period of a pendulum. State the effects also.  

 Q7. Distinguish between speed and velocity.

 Q8. A car is moving with a velocity of 20 m/s. The brakes are applied to retard it at a rate of 2m/s². What will be the speed after 5 s of applying the brakes? 

 Q9. What does the slope of following graphs represent? 

i) displacement-time  graph  ii) velocity-time graph 

  Q10. Derive the relation: S=ut + ½at² ( any method). 

Q11. A body moves from rest with a uniform acceleration and travels 270 m in 3 s. Find the velocity of the  body at 10 s after the start. 

Q12. Define: i) acceleration ii) acceleration due to gravity.

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Why are there only two types of electric charges?

There are two types of charges because we can establish charges only by loss or gain of electrons present in the orbits of an atom. 

By losing electrons  a body gets positively charged and by gaining electrons it gets negatively charged. 

Electron is the fundamental charge. It's taken as negatively charged. 

Why do you need moisturising cream in winter season?

 Q. Why do you need moisturising cream in winter season?

Answer: As the humidity is low in winter season where there is no winter rainfall, skin loses water due to evaporation and has tendency to dry quickly. To prevent this we need moisturising cream.

TRIBO-ELECTRIC SERIES

 TRIBO-ELECTRIC SERIES 

The series in which the substances are arranged according to their tendency to lose or gain electrons on rubbing each other. The higher the position of the substance, it has the tendency to lose electrons and to gain positive charge on rubbing.

The series of common substances  follows,

Air

Human hair

Rabbit's fur

Glass

Hair

Silk

Paper

Cotton

Steel

Wood

Amber

Rubber balloon

Plastic wrap

Ebonite

Example:

When glass rod is rubbed with silk, the rod loses electrons and get positively charged whereas silk gains electrons from the rod and gets negatively charged. Please check the position of glass in relation with silk. Glass is placed above silk.