Thursday, May 31, 2012

CBSE_NCERT Chapter_Shorting of material into group for class VI(6th) Science

Q. What is luster?

Ans: Materials around us have a particular type of shine called Luster like gold, silver, aluminum etc
Q. Some metal can hammered into thin sheet without breaking into pieces. Name this property of metals?
Ans: Malleability.
Q. Some metal drawn into thin wire. Name this property of metals? 
Ans: Ductility.
Q. Name material used to make chalk?
 Ans: Calcium carbonate
Q. Why do houses have cement floor? 
Ans: Houses have cement floor because it can polished to make attractive.
Q. Define soluble and insoluble substance?
Ans: Material that mixed with water is called soluble e.g. acid, base, milk, lemon juice, sugar and alcohol. Material that do not mixed with water is called insoluble like oil, sand, alum etc 

Q. what will happen if you drop piece of chalk and sponge in to glass of water?
Ans: Chalk and sponge absorb water due to gap between their particles.
Q. Which material you prefer to use for furniture?
Ans: Wood and Metal as they can polished and hard to break.

Q. Classify material on the basis of conductivity?
Ans: Materials have property to conduct electricity through them. This property is called conductivity. On the basis of that it can be divided into Good conductor and bad conductor.  A substance which conducts electricity is called good conductor like silver, copper, aluminum. 
Q. Name the best conductor metal?Ans: Silver is best conductor.
Q. Name a non metal that conduct current? 
Ans: Graphite is only non metal that conduct electricity.
Q. What is the name of material that can scratch easily? 
Ans: hard
Q. Name hardest and softest substance 
Ans: Diamond and talcum powder
Q. What does cold drink contains. 
Ans: carbon dioxide gas, sugar and flavored syrup.
Q.Why axe head is made up of iron?
Ans: Because iron is cheap, hard and malleable.
Q. Defines: Solute, solvent and solution?
Ans: Solution: The mixture of two or more substance is called solution. Solute: A substance that is being dissolved is called Solute. Solvent: The substance in which solute dissolve.
Q. Why ice floats on water?
Ans: The density of ice is lower than water so, Ice floats on water.
Q.What is transparency?
Ans: The property of substance to allow light to pass through is called transparency.
Q. What is Opaque object?
Ans: Object that do not allow light to pass is called opaque like wood, metals etc. Object that allow light to pass partially is called Translucent. Glass, water, Oil paper etc.
Q. Why handle of utensils made up of Plastic or wood?
Ans: This is because Plastic or wood is bad conductor of heat.
Q. What kind of substance do we see around us?
Ans: we have two types of substance like man Plastic or wood made and natural.
Q. Why do some substance sink or others floats to the beaker field with water?
Ans: Some substances do not dissolve in water so they float unless sink.
Q. Why we can smell something e.g. perfume?
Ans: we can smell something e.g. perfume because smell the liquid floats in the air when evaporated.

http://jsuniltutorial.weebly.com For: CBSE Class VI Science Notes , Test paper, AssignmentsWorksheets

Saturday, May 26, 2012

9th physics Force and laws of Motion solved questions

9th physics:  Force and laws of Motion

An object of mass 2 kg is sliding with a constant velocity of 4 m/ s on a frictionless horizontal table. The force required to keep the object moving with the same velocity is
(a) 32 N                                    (b) 0 N                          (c) 2 N                          (d) 8 N                          Ans: (b]       

Rocket works on the principle of conservation of
(a) mass                                   (b) energy                     (c) momentum               (d) velocity                     
Ans: [c]

A car is moving at 45 km/hr.A constant force acts on the car for 10 sc .So that it's velocity becomes 63 km/hr .The distance travelled by car during this interval of 10 sec is :
a) 100 m                                   b) 150 m                       c) 200 m                       d) 50 m                         Ans: [b]
    
What is the definition of balanced and unbalanced force?

Ans:  When two equal forces acting on an object in opposite directions called balanced force. When something does not move the forces are balanced, e.g. Gravity pulls a table down but that table is pushed up by the floor or the ground it stands on so doesn’t’ move.
An Unbalanced force is needed for something to change movement or change direction, e.g. a seesaw moving up and down because the forces are not equal.
Net force: - The sum of all the forces acting on a body is known as net force.

Difference between Balanced force and unbalanced force.

Ans:  Balanced force:- If net force on a body is zero it is called balanced force. Balanced forces do not cause a change in motion. They are equal in magnitude and opposite in direction. Therefore, the resultant of these forces will be zero.
Example: Two persons pushing a box with the same force in opposite directions.

Unbalanced forces:- If net force on a body is non-zero it is called unbalanced force.
Forces whose resultant is not equal to zero are called unbalanced forces. For example: An arm wrestling competition among a strong person and a weak one. The resultant force will be in the direction of the force applied by the strong person.

What Is Inertia

Ans: By Newton's law we know that ,a body at rest will remain at rest and a body in motion will continue in a straight line unless it is compelled by an external force.This tendency of a body is called inertia.So we can say that 'Inertia is that property of a body due to which it resists a change in its state of rest or of uniform motion.'

When the brakes are applied to the bike the back seater  moves forward why?

When the bike accelerates suddenly the back seater who was initially at rest experiences a force of friction at the point of contact between him and the bike. His inertia of rest tries to keep him at rest which results in a backward push. Thus, the back seater moves backwards when the bike accelerates suddenly.
                    When the brakes are applied the inertia of motion of the back seater tries to keep him in motion so he moves forward.

There are three solids made up of aluminium, steel and wood, of the same shape and same volume. Which of them would have highest inertia?

Ans: Since steel has greatest density and greatest mass, therefore, it has highest inertia.
As the mass is a measure of inertia, the ball of same shape and size, having more mass than other balls will have highest inertia.

Two balls of the same size but of different materials, rubber and iron are kept on the smooth floor of a moving train. The brakes are applied suddenly to stop the train. Will the balls start rolling? If so, in which direction? Will they move with the same speed? Give reasons for your answer

Ans: Yes. the balls will start rolling in the direction in which the train was moving.  Due to the application of the brakes, the train comes to rest but due to inertia the balls try to remain in motion, therefore, they begin to roll.

Since the masses of the balls are not the same, therefore, the inertial forces are also not same on both the balls. Thus, the balls will move with different speeds.

Horse need continues of force in order to move a cart with a constant speed. Why?
Horse need continues of force in order to move a cart with a constant speed to balances the force of friction.

Write a short note on third law of motion

Ans: Third law of motion : This law deals with the forces between bodies that appear in pairs. It says that “every action has an equal and opposite reaction” 
 When you stand on the ground, your weight pushes the ground downwards; does this make the ground to move downward? No, because the ground pushes you upward with a force equal to your weight and hence these equal and opposite forces cancel out and you stand on the ground balanced.
 Force by you on the ground and force on you by the ground are two equal and opposite forces acting in pairs at the surface that is common to both you and the ground.
Newton’s 3 rd law of motion is applicable wherever there is action-reaction force pair. Like walking, shooting with a pistol, collision, rocket propelling, etc.

How a karate player can break a pile of tiles with a single blow of his hand?

Ans:  Karate player strikes the piles in a very short time in a very small area.  Since, impulse, I = F × t Þ F = I/t.   If   ‘t’ will be very short the force becomes very large and act on smaller area .This produce enough pressure by his hand on break the brick

Define momentum?

Ans: Momentum (Linear momentum) for moving body is defined as the product of mass and velocity.  If a body is moving with velocity, v and having mass, m then momentum of body is p = m x v.
Momentum is a vector quantity. Its direction is the same as that of velocity. SI unit of momentum (p) is kg-m/s

Explain why it is easier to stop a tennis ball than a cricket ball moving with the same speed?

Cricket ball has more momentum than the tennis ball due to greater mass. That’s why it is easier to stop a tennis ball than a cricket ball moving with the same speed.

Why a goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal.

Ans: To reduce the force exerted by ball on hand by increasing time as F = I/t.

A passenger in a moving train tosses a coin which falls behind him. Why?

Ans: Because that motion of the train is accelerated.

State and explain the three laws of Newton?

Ans:  First law of motion: Newton’s First law explains the “natural” motion of an object when it is left free. The law says that- Every object continues in its state of rest, or of uniform motion in a straight line with unchanging speed, unless compelled to do otherwise by forces acting upon it.
So, naturally an object at rest will remain at rest and an object moving with a constant speed in a straight line will keep moving, unless they are disturbed by a force.
This property of matter to continue its state of rest or of uniform motion is called “Inertia”. Hence, this law is also called the Law of Inertia.
Second law of motion: Newton’s 2nd law of motion relates the external force (F) acting on a body with the mass (m) of the body; and is mathematically written as F = ma, ‘a’ is the acceleration of the body due to the force. It states that the acceleration of a body due to net external force acting on it is equal to the net force divided by the mass of the body.
The difficulty you face while pushing or pulling a heavier box compared to a lighter box is explained by the 2nd law of motion.
Third law of motion: This law deals with the forces between bodies that appear in pairs. It says that every action has an equal and opposite reaction. When you stand on the ground, your weight pushes the ground downwards; does this make the ground to move downward? No, because the ground pushes you upward with a force equal to your weight and hence these equal and opposite forces cancel out and you stand on the ground balanced. Force by you on the ground and force on you by the ground are two equal and opposite forces acting in pairs at the surface that is common to both you and the ground.

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Sunday, May 13, 2012

CBSE (VII)PHYSICS: Heat and Temperature for CBSE Science class VII


CLASS VII  Science (Physics) 

Chapter- Heat and Temperature 

Question with solution Part-1
 Q.1. What is heat?
Ans: Heat is form of energy that produces feeling of hotness. It is measured in Joule . Calorie is used to measure energy value of food. 1 cal. =4.2 joule
Q. 2.What is energy?
Ans: Energy is capacity to do work. Energy is neither created nor destroyed it can only changed one form to another.
Q. 3.What are the effects of heat?
Ans: Heat cause many change in living and non living thing. They are
1. Heat increase in temperature 
2. Heat expand a substance   
3. Heat changes the state   
4. Heat bring chemical change
5.Heat effect living thing
Q.4. What is temperature?
Ans: The degree of hotness and coldness of a body is called temperature of body. Thermometer is an instrument used to measure temperature. It is work on principle of expansion in liquid on heating. It is measured in Celsius and Fahrenheit scale but for scientific work Kelvin scale is used.
 0F = (9/5 x 0C) +32  and  oC = (9/5)(F- 32) and K= C + 273o
Q. 5.What is thermometry?
Ans: The science of measurement of temperature is known as thermometry
Q.6. What are different types of thermometer?
Ans: Thermometer: It consist of long narrow glass tube having fine bore.There is a glass bulb filled with liquid mostly mercury at the one end and sealed at other end. There is small bend just above bulb called Kink.  it does not allow the mercury to fall as soon as taken out from our mouth.
(i). Laboratory Thermometer: It ranges from -10oC to 110oC
(ii) Clinical thermometer: It is used to measure body temperature. It ranges from 35oC to 42oC and 94oF to 108oF.  Mercury thermometer can measure temperature from -35oC to 357oC.
(iii) Alcohol thermometer used to measure temp. from -125oC to 50oC.
Q. 7.What is the use of the m a x i m u m - m i n i m u m thermometer?
Ans:  The maximum and minimum temperatures atmosphere reported in weather reports which is measured by a thermometer called the m a x i m u m - m i n i m u m thermometer.
Q.8. What is the normal body temperature?   
Ans: 37oC or 98.6oF.
Q.9. Why mercury preferred in thermometers?
Ans: Mercury used due to following reasons
(i) It expand uniformly  
(ii) It does not stick to wall
 (iii) It is shiny and easy to see
 (iv) It remain liquid at room temperature.
Q.10. Find at what temperature measurement on Celsius equal to Fahrenheit.   
[Ans: - 400]
Q.11. Find at what temperature measurement on Fahrenheit double of Celsius
[Ans: 1600]
Q. 12.What is thermal expansion (enlargement)?
Ans: The expansion produced in substance on heating is called thermal expansion. When we heat a substance its molecules gain energy and start vibrating rapidly and spread out . As a result a substance expands.
Q.13. Why does gas expand more than solid and liquid?
Ans: Gas expands more than solid and liquid because its molecules are bound with very weak force of   attraction.
Q.14. A bimetallic strip made of brass and iron welded together. When it is heated, the strip bend why?
Ans: Brass expand and contract more than iron on heating and cooling. This unequal expansion and contraction bent the strip.
Q. 15.The same quantity of heat supplied to same amount of different substances does not necessarily produce the same increase in temperature. Why?
Ans: Different substances absorb differently that depends on
(a) Mass of body
(b) change in temperature
(c) Nature of substance. For this reason  the same quantity of heat supplied to same amount of different substances does not necessarily produce the same increase in temperature
Q.16. If difference in temperature between A and B is 50C , What is the difference in Kelvin?
Ans: 5K
Q.17. Give some examples expansion causes problems?
Ans (i). Gaps are left between two sections of railway tracks that allow expansion in summer and protect from bending causing accident.
(ii). During summer, iron expands and cause serious accidents. To allow this expansion Space left between two sections of rail tracks.
(ii). When we pour hot liquid, sometime glass tumbler crack because inner wall get heated quickly and expand than outer wall. A Pyrex glass resist from this unequal expansion.
Q. 18.Explain one  good use of expansion:
1. In fire alarm expansion put in good use. The alarm contains two strips of iron and brass bolted together. When it is heated because of fire, brass expands more than iron and bends towards iron. Bell starts ringing. As the fire put out strip gets cooled and straighten again.
Q.19. What is heat capacity?
Ans: The amount of heat required to raise temperature of a substance by 10C . It is different for different substance. It depends on (a) Mass of body (b) change in temperature (c) Nature of substance. µ m    and Q µ t    Þ Q = S m t
Here, S is a constant and named Specific heat of body.
Q. 20.What is specific heat capacity?
Ans. The amount of heat required to raise the temperature of 1 kg  by 10C . Water has highest heat capacity. SI unit is j/kg0C
Q.21. Define melting and boiling point
Ans .The temperature at which solid melts is called Melting point. Melting point of ice is 00C and wax is 630 C. The temperature at which liquid changes into vapour is called boiling point.
Q. 22.What is latent heat of fusion?
Ans: Latent heat or hidden is amount of heat that only change state not temperature.
The amount of heat required to melt 1 kg substance from solid to liquid without change of temperature is called latent heat of fusion.
Q. 23.What is latent heat of vaporization?
Ans: The amount of heat required to change 1 kg substance from liquid to vapour state without change of temperature is called latent heat of vaporization.
Q. 24.Why stem burn more than boiled water?
Ans: Because stem has more latent heat than boiled water[ about 2260j/g]
Q.25. why does water used as coolant in car?
 Ans: Water has high specific capacity this makes water to take long time to heat up by absorbing very large quantity of heat. Therefore water used as coolant in car and factories.
Q.26. What are different mode of transfer of heat?
Ans: Heat flows from higher to lower temperature till both body attend same temperature.
There are three mode of transfer of heat
(a) Conduction: The mode of transfer of heat from molecules to molecules without movement of particles.. Conduction takes place in solid as its molecules ate closely packed. Solids, metals and alloy are good conductor. Non metals, plastic glass are bad conductor of heat.
(b)Convection: The mode of transfer of heat from molecules to molecules with movement of particles. In liquids and gasses heat transferred by convection as molecules are far apart from each other .
(c) Radiation: The mode of transfer of heat that does not require any material medium. Heat of sun reach the earth by radiation.
Q.27. At what factor heat absorbed on radiation by body depends on?
Ans: (a) Distance between body and source of heat
(b) its colour(Black coloured surface absorb more than white surfaces)
Q. 29. A desert is very hot in the day and very cold at night?
Ans: Due to low specific heat capacity air above land heated up quickly in the day and cooled quickly at night. For this reason a desert is very hot in the day and very cold at night.
Q.30. Describe construction and working of thermos flask.
Ans: thermos flask is doubled walled glass vessel. Air inside glass wall prevents conduction and convection. Glass walls are silvered on the inside. Silver is good reflector of heat this prevent heat loss due to radiation. If we remove the silvering thermos flask not keep liquids hot or cold for quite a long time.