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.