PRACTICE WORKSHEET, CH 11, CLASS 6

A. Multiple Choice Questions

1. Shadows form because:
(a) opaque objects reflect light
(b) opaque objects do not allow light to pass through them
(c) light travels in one direction from a source
(d) light bends around an opaque object

2. objects do not allow any light to pass through them.
(a) Transparent
(b) Translucent
(c) Opaque
(d) Luminous

3. Which of the following is a non-luminous body?
(a) Moon
(b) Sun
(c) Bulb
(d) Burning candle

4. The colour of a shadow is :
(a) black
(b) green
(c) grey
(d) cannot say

5. The speed of light in vacuum is :
(a) 3 × 108 m/sec
(b) 2 × 109 m/sec
(c) 1.5 × 108 m/sec
(d) none of these

B. Fill in the Blanks:

1. Light is a form of ……………………. .
2. A glowing tubelight is an example of …………………… source of light.
3. The shadow of an object is always of ………………. colour.
4. The …………………… is a luminous object.
5. Light travels in a ……………….. line.

C. State True or False:

1. The moon is a natural source of light. ……………….
2. Light always travels in a straight line. ……………….
3. Pinhole camera works on the principle of rectilinear propagation of light. ………………….
4. Stars are luminous bodies. …………………
5. Shadow of an object is formed in the direction. opposite to that of the light source. …………….

D. Match the following:

‘A’	‘B’
1. Brick	a. A natural source of light
2. Tubelight	b. Region of partial darkness
3. Sun	c. Shadow cast by heavenly bodies
4. Eclipse	d. An opaque object
5. Penumbra	e. An artificial source of light

E. Write the letter in the blanks given below with the help of corresponding hints.

1. T _ _ _ S _ _ _ _ _T.
Hint: Through these objects, we can see but not very clearly.

2. _ _M _ N _ _ S.
Hint: Sun is in this category of sources of light.

3. S _ R _ _ _.
Hint: We can’t obtain an image without this.

4. R _ _ _ C _ _ _ _ .
Hint: Mirror gives us clear images because of this phenomenon.

Class 8 Chapter 12 Friction, NCERT Solutions

 1. Fill in the blanks.

(a) Friction opposes the _____________ between the surfaces in contact with each other.

(b) Friction depends on the _____________ of surfaces.

(c) Friction produces __________.

(d) Sprinkling of powder on the carrom board ________ friction.

(e) Sliding friction is ___________ than the static friction.

Soln:

(a) Friction opposes the motion between the surfaces in contact with each other.

(b) Friction depends on the nature of surfaces.

(c) Friction produces heat.

(d) Sprinkling of powder on the carrom board reduces friction.

(e) Sliding friction is lesser than the static friction.

2. Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.

(a) rolling, static, sliding

(b) rolling, sliding, static

(c) static, sliding, rolling

(d) sliding, static, rolling

Soln:

Answer is (c) static, sliding, rolling

3. Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be

(a) wet marble floor, dry marble floor, newspaper and towel.

(b) newspaper, towel, dry marble floor, wet marble floor.

(c) towel, newspaper, dry marble floor, wet marble floor.

(d) wet marble floor, dry marble floor, towel, newspaper

Soln:

Answer is (a) wet marble floor, dry marble floor, newspaper and towel.

4. Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.

Soln:

When book slides down on the desk, a frictional force acts between the book and the surface of the desk. The direction of the friction force on the book is opposite to the direction of its motion and acts in an upward direction. It is shown in the diagram below.

5. You spill a bucket of soapy water on a marble floor accidently. Would it make it easier or more difficult for you to walk on the floor? Why?

Soln:

It is possible to walk on the floor because of the friction present between our feet and the ground. For walking, we push the ground in a backward direction with our feet. The force of friction pushes it in the forward direction and allows us to walk. The force of friction decreases between the ground and the feet when there is soapy water spilt on the floor. Hence, it becomes difficult to walk on the soapy floor.

6. Explain why sportsmen use shoes with spikes.

Soln:

Sportsmen use shoes with spikes because of the better grip given by spikes while running. This is because the force of friction between the shoes and the ground increases with the help of spikes.

7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

Soln:

Due to the interlocking of the irregularities on the two surfaces in contact, the force of friction arises. On the floor when a heavy object is placed, the interlocking of irregularities on the surface of the box and floor become strong. This is because the two surfaces in contact are pressed harder. Hence, more force is required to overcome the interlocking. Thus, to push the heavier box, Seema has to apply greater force than Iqbal.

8. Explain why sliding friction is less than static friction

Soln:

When irregularities present in the surfaces of two objects in contact get interlocked with each other, friction come into play.  The time given in sliding for interlocking is very small. Thus, interlocking is not strong. Therefore, less force is required to overcome this interlocking. Due to this reason, sliding friction is less than static friction.

9. Give examples to show that friction is both a friend and a foe.

Soln:

Advantages of the friction

a) Due to friction, we are able to walk.

b) We are able to write because of the friction between the tip of the pen and paper.

Disadvantages of friction

a) Because of friction, the tires and soles of shoes wear out.

b) Friction produces heat between different parts of the machines. This can damage the machines.

10. Explain why objects moving in fluids must have special shapes.

Soln:

When a body moves through a fluid, it experiences an opposing force which tries to oppose its motion through the fluid. This opposing force is known as the drag force. This frictional force depends on the shape of the body. By giving the objects a special shape, the force of friction acting on it can be minimized. Hence, it becomes easier for a body to move through the fluid.

Class 6 Science Chapter 10 Motion and Measurement of Distances

 1. Give two examples each, of modes of transport used on land, water and air.

Solution:

Land- Train, Bus

Water- Ship, Boat

Air- Helicopter, Aeroplane

2. Fill in the blanks:

(i) One metre is ______________ cm.

(ii) Five kilometre is ______________ m.

(iii) Motion of a child on a swing is ______________.

(iv) Motion of the needle of a sewing machine is ______________.

(v) Motion of wheel of a bicycle is______________.

Solution:

(i) One metre is 100 cm.

(ii) Five kilometre is 5000 m.

(iii) Motion of a child on a swing is periodic.

(iv) Motion of the needle of a sewing machine is periodic.

(v) Motion of the wheel of a bicycle is circular.

3. Why can a pace or a footstep not be used as a standard unit of length?

Solution:

Pace or a footstep cannot be used as a standard unit of length because it varies from person to person.

4. Arrange the following lengths in their increasing magnitude: 1 metre, 1 centimetre, 1 kilometre, 1 millimetre.

Solution:

1 millimetre, 1 centimetre, 1 metre, 1 kilometre

5. The height of a person is 1.65 m. Express it into cm and mm.

Solution:

1.65= 165 cm = 1650 mm

6. The distance between Radha’s home and her school is 3250 m. Express this distance into km.

Solution:

1km = 1000 m

Hence 3250 m = 3.25 kms

7. While measuring the length of a knitting needle, the reading of the scale at one end is 3.0 cm and at the other end is 33.1 cm. What is the length of the needle?

Solution:

Length of needle = 33.1 – 3 = 30.1 cm

8. Write the similarities and differences between the motion of a bicycle and a ceiling fan that has been switched on.

Solution:

Similarities – The blades of a fan and the wheels of a bicycle shows circular motion

Differences- Bicycle move in rectilinear motion, but the fan does not move in rectilinear motion.

9. Why would you not like to use a measuring tape made of an elastic material like rubber to measure distance? What would be some of the problems you would meet in telling someone about a distance you measured with such a tape?

Solution:

An elastic measuring tape will not give accurate measurement as it stretches in length and reduces in size when stretched. When we express measurement taken with elastic tape, we have to tell whether the tape was stretched. If yes, how much. Hence it is very difficult to tell the measurement taken from an elastic tape.

10. Give two examples of periodic motion.

Solution:

a) A needle of a sewing machine

b) Pendulum

Class 6 Science Chapter 11, NCERT Back Exercise

 1. Rearrange the boxes given below to make a sentence that helps us understand opaque objects.

Solution:

The given boxes can be rearranged to form ‘Opaque Objects Make Shadows’ as shown below

2. Classify the objects or materials given below as opaque, transparent or translucent and luminous or non-luminous:

Air, water, a piece of rock, a sheet of aluminum, a mirror, a wooden board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, a piece of red hot iron, an umbrella, a lighted fluorescent tube, a wall, a sheet of carbon paper, the flame of a gas burner, a sheet of cardboard, a lighted torch, a sheet of cellophane, a wire mesh, kerosene stove, sun, firefly, the moon.

Solution:

Opaque:  A piece of rock, a sheet of aluminium, a mirror, a wooden board, a CD, an umbrella, a wall, a sheet of carbon paper,  a sheet of cardboard.

Transparent: Air, water, a sheet of plane glass.

Translucent: A sheet of polythene, smoke, fog, a sheet of cellophane, a wire mesh.

Luminous: A piece of red hot iron, a lighted fluorescent tube, the flame of a gas burner, a lighted torch, sun, firefly, kerosene stove.

Non – luminous: Air, water, a piece of rock, a sheet of aluminium, a mirror, a wooden  board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, an umbrella, a wall, a sheet of carbon paper, a sheet of cardboard, a sheet of cellophane, a wire mesh, moon.

3. Can you think of creating a shape that would give a circular shadow if held in one way and a rectangular shadow if held in another way?

Solution:

Yes,

4. In a completely dark room, if you hold up a mirror in front of you, will you see a reflection of yourself in the mirror?

Solution:

No, in a dark room, a mirror reflection of the image will not be shown as the light will not fall on the mirror to reflect the image due to darkness.

CCT Practice Paper, Class VIII SCIENCE, Ch 8

Basic features of cells

All cells are bounded by a plasma membrane. The semifluid substance within the membrane is the cytosol, containing the organelles. All cells contain chromosomes which carry genes in the form of DNA. All cells also have ribosomes, tiny organelles that make proteins using the instructions contained in genes. A major difference between prokaryotic and eukaryotic cells is the location of chromosomes. Eukaryotic cell- chromosomes are contained in a membrane-enclosed organelle, the nucleus. Prokaryotic cell- the DNA is concentrated in the nucleoid without a membrane separating it from the rest of the cell.

  

Fig.1 Bacteria Problems with Cell Size

In general, eukaryotic cells are much bigger than prokaryotic cells: Most bacteria are 1-10 microns in diameter. Eukaryotic cells are typically 10-100 microns in diameter. A large cell requires "much more" in terms of the cellular components. Uptake from the environment is also a problem for large cells: there is less surface area compared to the volume. Distribution of nutrients from one portion of a large cell to another is also a problem, simply because of the distance required for the nutrients to travel. 

Fig 2

Thus most cells are small: sufficient surface area to accommodate the volume. Larger organisms do not generally have larger cells than smaller organisms, - just simply more cells.

Question 1.What will be the size range of bacteria in millimeter?  (1 micron= 10-3 mm)

1. 103mm-102mm

2. 10-3mm-10-2mm

3. 102mm-103mm

4. 10-2mm-10-3mm

Question 2 .(a)The cells can be Prokaryotic or Eukaryotic .Fig. 1 explains the structure of which type?

                      -------------------------

Question 3 Why cells are preferred to be of small size? Write two reasons.

                       -------------------------------------------------------------

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Question 4 The DNA present in the cell signifies chemical nature of--

1. Genes

2. Chromosomes

3. Ribosomes

4. Prokaryotes

Choose the correct option-

1. a and c

2. b and d

3. a and b

4. c and d

Class XII Biotech ONE WORD Practice Questions, PROTEIN STRUCTURE AND ENGINEERING (INTRODUCTION, STR-FUN. RELATIONSHIP),

 

GREEN OLYMPIAD BY TERI

 As per the letter recieved by KVS it is for the information of students that to inform that TERI is going to organize an Environmental theme based 'Green Olympiad 2021' in online mode is to be conducted by on  10-21 November 2021 & 6-17 December 2021 for the students from classes IV toXII. Registration for the competition is to be done from 15 August to 30th September 2021on the link given below. :

www.teriin.org/olympiad

It is requested that the Principals of the Vidyalayas under the region may be informed toencourage the students to participate in the said competition on VOLUNTARY BASIS.

FOR INDIVIDUAL REGISTRATION YOU CAN VISIT 

https://www.teriin.org/olympiad/registration/iregistration.php

Solutions of NCERT Exemplar Solutions for Class 6 Chapter 8 – Body Movement

 1. Solution:

(a): (i) and (iii)

Bones form the structural framework of a body called a skeleton. The skeleton along with muscles helps our body parts to move. Bones are hard and cannot bend on their own. The joints help the body in moving.

Muscles are like elastic bands which are attached to the bones by means of tough connecting bands called tendons. Muscles help in the movement of bone through pull/contraction. Bones are wrapped up by muscles.

2. Solution:

(c): Upper jaw and skull

Upper jaw and skull have immovable joints since they are fixed joints.

3. Solution:

None.

Human beings and dogs have endoskeleton and muscles.

Snails have exoskeleton and muscles.

Earthworm does not have a skeleton. It has two sets of muscles one that makes it long and thin and the other that makes it fat. The contraction and relaxation of

these muscles help in movement.

4.  Solution:

(a): swim easily in water

Divers while swimming wears fin-like flippers on their feet because the muscle in the feet contracts, generating a curve on one side like a wave and the fin-like flippers move on the opposite direction exerting force against the surrounding water that pushes the underwater divers forward.

5. Solution:

(c): muscular foot

The muscular foot of the snail comes outside and attaches to the ground during locomotion. The foot of a snail has a special gland that produces slimy mucus to make slippery track to help it move smoothly.

6. Solution:

(b): Two

7. Solution:

Hinge joints present in our fingers help us to grasp the things like badminton racquet.

8. Solution:

If our backbone was made of one single bone we would not have been able to bend and twist our back.

9. Solution:

Here are the one-word answers:

1. Ball and socket joint
2. Bone
3. Upper jaw with the skull
4. Muscles
5. Ribs
6. Skeleton
7. Pelvic bones
8. Pivotal joint
9. Cartilage

10. Solution:

(a) Hinge joint and ball and socket joint

(b) Pivotal joint

(c) Hinge joint

NCERT Exemplar Solutions for Class 6 Chapter 8 – Body Movement

 Multiple Choice Questions:

1. Which of the following parts of our body help us in movement?
(i) Bones
(ii) Skin
(iii) Muscles
(iv) Organs
choose the correct answer from the option below.
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (iv)
(d) (ii) and (iii)

2. Which of the following joints is immovable?
(a) Shoulder and arm
(b) Knee and joint
(c) Upper jaw and skull
(d) The lower jaw and upper jaw

3. Which of the following organisms does not have both muscles and skeleton for movement?
(a) Dog
(b) Snail
(c) Earthworm
(d) Human being

4. Underwater divers wear fin-like flippers on their feet to
(a) swim easily in water
(b) look like a fish
(c) walk on the water surface
(d) walk over the bottom of the sea (sea bed).

5. A snail moves with the help of its
(a) shell
(b) bone
(c) muscular foot
(d) whole body.

6. How many muscles work together to move a bone?
(a) One
(b) Two
(c) Three
(d) Four

Very Short Answer Questions:

7. Name the type of joint of your hand which helps you to grasp a badminton racquet.

8. What would have happened if our backbone was made of one single bone?

9. Provide one-word answers to the statements given below.

1. A joint which allows movement in all directions.
2. A hard structure that forms the skeleton.
3. Part of the body with a fixed joint.
4. Help in the movement of the body by contraction and relaxation.
5. Bones that join with chest bone at one end and to the backbone at the other end.
6. A framework of bones which gives shape to our body.
7. Bones which enclose the organs of our body that lie below the abdomen.
8. Joint where our neck joins the head.
9. Part of the skeleton that forms the earlobe.

10. Write the type of joint which is used for each of the following movements.
(a) A cricket bowler bowls the ball.
(b) A girl moves her head in right and left direction.
(c) A person lifts weights to build up his biceps.

Solutions of NCERT Exemplar Class 8 Chapter 11 – Force And Pressure

 1. Soln:

Answer is (a) Magnitude of force applied by A is greater than that of B.

Explanation:

The magnitude of force applied by A is bigger than that of B as a result of the block moves towards right i.e. towards B.

2. Soln:

Answer is (c) magnetic force alone

Explanation:

As electric current flows through the coil it behaves like an electromagnet which creates magnetic force. Hence the answer is magnetic force alone.

3. Soln:

The answer is (b) electrostatic force.

Explanation:

On combing the hair, comb and hair get oppositely charged due to electrostatic force.

4. Soln:

The answer is (d) Pressure at A < Pressure at B

Explanation:

Increase in water leads to an increase in depth.

5. Soln:

The answer is (d) either a magnetic or an electrostatic force

Explanation: when two objects are experiencing repulsive force because there may be an electrostatic force or a magnetic force.

6. Soln:

The answer is (b) force of friction

Explanation:

Force of attraction acts only when the bodies are in contact.

7. Soln:

Answer is (a) B and C

Explanation:

B and C are at the same level, hence pressure will be the same at B and C.

8. Soln:

Answer is (a) maximum in position A-C

Explanation:

Since the area of contact is minimum pressure will be maximum in A.

9. Soln:

Muscular Force.

10. Soln:

While walking we apply force on the ground.

11. Soln:

Towards the east.

12. Soln:

Answer is Magnetic force.

13. Soln:

Answer is Electrostatic force

14. Soln:

Force of gravity.

15. Soln:

Yes, the force of gravity act on dust particles.

NCERT Exemplar Class 8 Chapter 11 – Force And Pressure

Multiple Choice Questions

1. In Fig 11.1, two boys A and B are shown applying force on a block. If the block moves towards the right, which one of the following statements is correct?

(a) The magnitude of force applied by A is greater than that of B.

(b) The magnitude of force applied by A is smaller than that of B.

(c) The net force on the block is towards A.

(d) The magnitude of force applied by A is equal to that of B.

2. In the circuit shown in Fig.11.2, when the circuit is completed, the hammer strikes the gong. Which of the following force is responsible for the movement of the hammer?

(a) gravitational force alone

(b) electrostatic force alone

(c) magnetic force alone

(d) frictional force alone

3. During dry weather, while combing hair, sometimes we experience hair flying apart. The force responsible for this is

(a) force of gravity.

(b) electrostatic force.

(c) the force of friction.

(d) magnetic force.

4. Fig.11.3 shows a container filled with water. Which of the following statements is correct about the pressure of water?

Soln:

 (a) The pressure at A > Pressure at B > Pressure at C.

(b) The pressure at A = Pressure at B = Pressure at C.

(c) The pressure at A <  Pressure at B > Pressure at C.

(d) The pressure at A <  Pressure at B.

5. Two objects repel each other. This repulsion could be due to

(a) frictional force only

(b) electrostatic force only

(c) magnetic force only

(d) either a magnetic or an electrostatic force

6. Which one of the following forces is a contact force?

(a) force of gravity

(b) force of friction

(c) magnetic force

(d) electrostatic force

7. A water tank has four taps fixed at points A, B, C, D as shown in Fig. 11.4. The water will flow out at the same pressure from taps at

(a) B and C

(b) A and B

(c) C and D

(d) A and C

8. A brick is kept in three different ways on a table as shown in Fig. 11.5. The pressure exerted by the brick on the table will be

(a) maximum in position A-C

(b) maximum in position B

(c) maximum in position

(d) equal in all cases.

Very Short Answer Questions

9. A ball of dough is rolled into a flat chapatti. Name the force exerted to change the shape of the dough.

10. Where do we apply a force while walking?

11. A girl is pushing a box towards the east direction. In which direction should her friend push the box so that it moves faster in the same direction?

12., In the circuit shown in Fig.11.6, when the key is closed, the compass needle placed in the matchbox deflects. Name the force which causes this deflection.

13. During dry weather, clothes made of synthetic fibre often stick to the skin. Which type of force is responsible for this phenomenon?

14. While sieving grains, small pieces fall down. Which force pulls them down?

15. Does the force of gravity act on dust particles?