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  bo...

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. 

 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  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.

 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.