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A free printable book

Science for classes 6 to 8

4 lessons, each with worked examples, a try-at-home activity and a practice sheet. The practice sheets are together after the lessons, and the answer keys are at the very back.

  • Science
  • Classes 6-8
  • 4 lessons
  • 40 practice questions
  • Free to print

Contents

Free learning for kids, Gurukul Technicals Institute. Printed from engineergurukul.com/resources/kids/books/science-6-8/

Contents

What is in this book

  1. 1Simple electric circuitsBuild a safe circuit with a cell, bulb and switch, and learn about conductors, insulators and why a circuit must be closed.6 min
  2. 2Light, shadows and reflectionLearn how light travels in straight lines, why objects make shadows, and how a mirror reflects light and flips left and right.5 min
  3. 3Separating mixturesLearn how to separate mixtures with hand-picking, winnowing, sieving, sedimentation, filtration, evaporation and magnets.5 min
  4. 4How plants make food: photosynthesisFind out how green leaves use sunlight, water and carbon dioxide to make food and give out oxygen: photosynthesis.4 min

Every lesson here can also be read on its own page, with links to related lessons. All printable books.

Lesson 1 of 4

Simple electric circuits

Build a safe circuit with a cell, bulb and switch, and learn about conductors, insulators and why a circuit must be closed.

Open this lesson on its own page · Practice sheet · Answer key · Contents

Let us begin

The big idea

When you press a switch, a bulb lights up as if by magic. It is not magic. It is a circuit. A circuit is a complete path for electricity to flow around. Here we use only a small torch cell, which is safe.

An electric cell has two ends, called terminals. One is positive (+) and the other is negative (−). The cell pushes electric current around a circuit. A torch uses one or more cells.

A simple circuit has a cell, wires, a bulb and a switch. The current flows from the positive terminal through the wires and bulb and returns to the negative terminal. The bulb glows when current passes through its filament.

A circuit must make a complete loop. When the switch is ON (closed), the path is complete and the bulb glows. When the switch is OFF (open), there is a gap, so no current flows and the bulb does not glow.

Materials that let electric current pass through them are called conductors. Metals like copper, aluminium and iron are good conductors. Materials that do not let current pass are insulators. Plastic, rubber, wood, glass and cloth are insulators.

When two cells are joined one after another, the positive end of one touching the negative end of the next, the total is the sum of their voltages. Two 1.5 V cells joined this way give 3 V. SAFETY: Only ever use small cells or torch batteries for experiments. Never touch a plug point, a switch board or mains electricity. It is dangerous and can kill.

A simple electric circuitA rectangle of wires. On the left is a cell with a longer line for the positive end and a shorter thick line for the negative end. On top is a closed switch. On the right is a glowing bulb with short rays. An arrow on the top wire shows the current going from the positive end of the cell, through the switch to the bulb. + − Cell Switch (closed) Bulb Current Wires
The current goes round a complete loop: cell, switch, bulb and back to the cell.

Worked examples

See how it works

  1. Will the bulb glow?

    A cell, a bulb and a switch are joined in a loop with wires. The switch is OFF. There is a gap in the loop, so the circuit is open and the bulb does not glow. When the switch is turned ON, the loop is complete and the bulb glows.

  2. Conductor or insulator?

    Test a key, an eraser, a coin and a plastic spoon in a circuit gap. The key and the coin are metal, so the bulb glows: they are conductors. The eraser and plastic spoon are insulators: the bulb stays off.

  3. Two cells together

    Two cells of 1.5 V each are joined end to end (positive to negative). Total voltage = 1.5 V + 1.5 V = 3 V. The bulb would glow brighter than with one cell, as long as the bulb is made for it.

Try it at home

Light a bulb and test conductors

You will need

  • One 1.5 V torch cell
  • One small torch bulb (with holder if you have one)
  • Two pieces of insulated wire with the ends bare
  • Sticky tape
  • Things to test: coin, key, eraser, plastic spoon, paper clip, wooden stick

What to do

  1. Tape one wire to the (+) end of the cell, the end with the small knob, and another wire to the flat (−) end.
  2. Touch the free end of one wire to the bottom tip of the bulb and the free end of the other wire to the side of the bulb. The bulb should glow, so you know your circuit works.
  3. Now lift one wire off the bulb. Touch that wire to one end of a test object, and touch the other end of the object to the bulb, so the object is part of the loop.
  4. Watch the bulb. If it glows, the object is a conductor. If it stays off, it is an insulator.
  5. Write a table of what you tested.

Ask a grown-up: An adult should strip the wire ends and help hold the bulb. Use ONLY a single 1.5 V cell. Never use mains electricity, a plug point, a phone charger or a vehicle battery for this experiment.

Fun fact

The first electric battery was made by the Italian scientist Alessandro Volta around the year 1800.

Lesson 2 of 4

Light, shadows and reflection

Learn how light travels in straight lines, why objects make shadows, and how a mirror reflects light and flips left and right.

Open this lesson on its own page · Practice sheet · Answer key · Contents

Let us begin

The big idea

We see a mango because light bounces off it and enters our eyes. Light also makes shadows and helps us see ourselves in a mirror. Let us look at how light behaves.

Objects that give out their own light, like the Sun, a flame and a torch, are called luminous. Objects like a book or a chair do not give out light. We see them only when light from another source falls on them and bounces into our eyes.

Light travels in straight lines. You cannot see around a corner for this reason.

Materials are of three kinds. Transparent materials let almost all light pass through, like clear glass. Translucent materials let some light pass, like butter paper. Opaque materials let no light pass, like wood, metal and cardboard.

A shadow forms when an opaque object blocks light. The shadow is the dark space behind the object, where the light cannot reach. A shadow is bigger when the object is nearer the light source and smaller when it is farther away.

When light falls on a smooth shiny surface like a mirror, it bounces back. This is reflection. In a plane (flat) mirror, the angle of incidence is equal to the angle of reflection. Both angles are measured from the normal, an imaginary line at right angles to the mirror. The image in a plane mirror is the same size as the object, but left and right are swapped. This is called lateral inversion. That is why the word AMBULANCE is printed reversed on the front of an ambulance, so that drivers see it correctly in their mirrors.

How a shadow formsA light source on the left sends straight rays to the right. An opaque object in the middle blocks the central rays. On the wall on the right, a dark patch called the shadow appears where the light is blocked, with lit areas above and below it. Light source Opaque object Wall Shadow
Light travels in straight lines. An opaque object blocks it and leaves a shadow.

Worked examples

See how it works

  1. Transparent, translucent or opaque?

    A clear glass window is transparent. Butter paper is translucent: you can see a blurry shape through it. A wooden door is opaque: you cannot see through it at all.

  2. Reflection angles

    A ray of light hits a plane mirror at an angle of incidence of 40°. By the law of reflection, the angle of reflection is also 40°. The angle between the incoming ray and the reflected ray is 40° + 40° = 80°.

  3. Size of a shadow

    You hold a toy near a lit torch and the shadow on the wall is large. You move the toy towards the wall, away from the torch, and the shadow becomes smaller.

Try it at home

Shadow play and see-through test

You will need

  • A torch
  • A plain wall in a dim room
  • A cardboard cut-out or a toy
  • Butter paper or thin paper
  • A clear plastic bag or glass
  • A flat mirror

What to do

  1. In a dim room, shine the torch on the wall and hold the toy between the torch and the wall.
  2. Move the toy closer to the torch, then closer to the wall. Notice how the shadow size changes.
  3. Hold butter paper, clear plastic and cardboard one at a time in front of the torch. Which ones let light through?
  4. Write down: transparent, translucent or opaque.
  5. Hold a word in front of a mirror and see how it is flipped left to right.

Ask a grown-up: Do the activity indoors with a torch. NEVER look at the Sun or shine a torch or laser straight into anyone's eyes.

Fun fact

Light travels about 3 lakh kilometres in one second.

Lesson 3 of 4

Separating mixtures

Learn how to separate mixtures with hand-picking, winnowing, sieving, sedimentation, filtration, evaporation and magnets.

Open this lesson on its own page · Practice sheet · Answer key · Contents

Let us begin

The big idea

Dal with stones in it, muddy water, and salt dissolved in sea water are all mixtures. We often need to separate the things in a mixture. Different mixtures need different methods.

A mixture has two or more substances mixed together, each keeping its own properties. Choosing a method to separate a mixture depends on how the parts differ.

Hand-picking removes bigger bits, like stones from rice or dal. Winnowing separates light husk from heavier grain: the mixture is dropped in the wind or a fan breeze, and the husk blows away. Sieving separates smaller pieces from bigger ones, like flour from bran. A magnet can pull out iron or steel pieces from other things.

Sedimentation and decantation: when muddy water stands, the heavy mud settles at the bottom. This is sedimentation. Pouring off the clear water on top, without disturbing the mud, is decantation.

Filtration uses a filter such as a cloth or filter paper. The liquid passes through but solid bits stay on it. A tea strainer filters tea leaves from tea.

Evaporation separates a dissolved solid from a liquid. When salt water is left in the sun, the water evaporates into the air and the salt is left behind. This is how common salt is made from sea water in salt pans. Sometimes more than one method is used. For a mixture of sand and salt, we dissolve the salt in water, filter out the sand, and then evaporate the water to get back the salt.

Worked examples

See how it works

  1. Choosing the method

    Stones in rice: hand-picking. Husk in wheat grains: winnowing. Iron nails in sand: a magnet. Tea leaves in tea: filtration through a strainer.

  2. Muddy water

    Let the muddy water stand. The mud settles (sedimentation). Pour off the clearer water from the top (decantation). To make it clearer still, pour it through a clean cloth (filtration). The water is still not safe to drink until it has been boiled.

  3. Sand and salt

    Step 1: add water to the mixture and stir. The salt dissolves. Step 2: filter. The sand stays on the filter and the salt solution passes through. Step 3: heat the salt solution or leave it in the sun until the water evaporates. The salt remains.

Try it at home

Clean muddy water

You will need

  • Two clear glasses or jars
  • A little soil
  • Water
  • A clean cotton cloth or paper kitchen towel
  • A rubber band
  • A shallow plate

What to do

  1. Mix a spoonful of soil in a glass of water and stir.
  2. Leave it for 20 minutes. Look at the soil that has settled at the bottom.
  3. Pour the top water slowly into the second glass without disturbing the soil. This is decantation.
  4. Fix the cloth over the mouth of a clean glass with the rubber band. Pour the cloudy water through it slowly.
  5. Dissolve a pinch of salt in a little water, pour it on a plate and leave it in the sun for a day or two. Look at the white salt left behind.

Ask a grown-up: The filtered water is NOT safe to drink. Do not taste it. No heating is needed for this activity.

Fun fact

In many coastal places in India, salt is made by letting sea water dry in the sun in large shallow pans.

Lesson 4 of 4

How plants make food: photosynthesis

Find out how green leaves use sunlight, water and carbon dioxide to make food and give out oxygen: photosynthesis.

Open this lesson on its own page · Practice sheet · Answer key · Contents

Let us begin

The big idea

Animals must find their food, but green plants make their own. They do this in their leaves, using sunlight. This process is called photosynthesis, and it also gives us the oxygen we breathe.

Photosynthesis means making food using light. It happens mainly in the leaves. The word comes from photo (light) and synthesis (putting together).

A plant needs three things: sunlight, water and carbon dioxide. The roots take in water from the soil, and it travels up the stem to the leaves. Carbon dioxide enters from the air through tiny holes on the leaf called stomata.

Leaves contain a green substance called chlorophyll. It traps the energy of sunlight. This energy joins water and carbon dioxide together to make glucose, a kind of sugar, and oxygen. The oxygen goes out into the air through the stomata.

In words: carbon dioxide + water → glucose + oxygen, in the presence of sunlight and chlorophyll.

Plants use some glucose for energy and to grow. The rest is stored as starch, in roots, seeds and fruits, like in potato and rice. Photosynthesis is important because nearly all food chains start with plants, and plants also add oxygen to the air.

Photosynthesis in a leafA green leaf in the middle. Sunlight arrives from the Sun at top left. Carbon dioxide arrives from the left. Water comes up from the bottom. Oxygen leaves to the right. Inside the leaf are the words: leaf makes glucose (food). Sunlight Leaf makes glucose (food) Carbon dioxide (from air) Water (from the soil) Oxygen
Sunlight, carbon dioxide and water go in. Glucose is made and oxygen comes out.

Worked examples

See how it works

  1. Chemical equation

    6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (with sunlight and chlorophyll). Check the atoms. Left: C = 6, H = 12, O = 12 + 6 = 18. Right: C = 6, H = 12, O = 6 + 12 = 18. Both sides match, so it is balanced.

  2. What does a plant need?

    A plant kept in a dark cupboard for many days cannot make food well, because there is no light. Its leaves turn pale and it grows weak.

  3. Where does each thing enter?

    Water comes in through the roots. Carbon dioxide comes in through the stomata in the leaves. Sunlight falls on the leaves. Oxygen leaves through the stomata.

Try it at home

Seedlings in light and in the dark

You will need

  • Moong (green gram) seeds, soaked overnight
  • Two small cups with wet cotton wool or wet paper towel
  • A bright windowsill
  • A dark cupboard
  • Water

What to do

  1. Put soaked seeds on the wet cotton in each cup.
  2. Place one cup on a sunny windowsill and the other inside a dark cupboard.
  3. Sprinkle a little water on both every day. Keep the cotton just wet, not soaking.
  4. After 5 to 7 days, take the dark-cupboard cup out and compare the two sets of seedlings.
  5. Which seedlings look greener and which look pale and thin? Write down why.

Ask a grown-up: Please help to keep the cotton damp, and wash the cups after the activity.

Fun fact

Plants and the green algae in oceans together make much of the oxygen in the air we breathe.

Part two

Practice sheets

One sheet for each of the 4 lessons. Write your name and the date at the top, answer in the spaces, then check with the answer keys at the back.

Practice sheet

Simple electric circuits

Practice sheet: Simple electric circuits (Classes 6-8, Science)

  1. What are the two ends of a cell called?
  2. Name the four parts of a simple circuit that we use to light a bulb.
  3. Will a bulb glow if the switch is open? Why or why not?
  4. What is a conductor? Give one example.
  5. What is an insulator? Give one example.
  6. Which of these is a conductor: rubber, copper, wood?
  7. Why are electric wires covered with plastic or rubber?
  8. Two 1.5 V cells are joined end to end (positive to negative). What is the total voltage?
  9. Why must a circuit be a complete loop?
  10. Why should we never experiment with the mains electricity from a socket?

Practice sheet

Light, shadows and reflection

Practice sheet: Light, shadows and reflection (Classes 6-8, Science)

  1. Name one luminous object.
  2. In what kind of path does light travel?
  3. Is clear glass transparent, translucent or opaque?
  4. Is butter paper transparent, translucent or opaque?
  5. What type of material forms a clear, dark shadow: transparent or opaque?
  6. What happens to the size of a shadow when you move the object nearer to the torch?
  7. What do we call the bouncing back of light from a mirror?
  8. A ray of light hits a mirror with an angle of incidence of 35°. What is the angle of reflection?
  9. The angle of incidence is 50°. What is the angle between the incident ray and the reflected ray?
  10. Why is the word AMBULANCE written reversed on the front of an ambulance?

Practice sheet

Separating mixtures

Practice sheet: Separating mixtures (Classes 6-8, Science)

  1. Name a method to remove stones from rice.
  2. Which method separates husk from grains using the wind?
  3. Which method would you use to separate iron filings from sand?
  4. What is sedimentation?
  5. What is decantation?
  6. What do we use to filter tea leaves out of tea?
  7. Which method separates salt from salt water?
  8. You have a mixture of sand, salt and water. Which method removes the sand?
  9. Give the steps to get dry salt from a mixture of sand and salt.
  10. Why is filtered pond water still not safe to drink?

Practice sheet

How plants make food: photosynthesis

Practice sheet: How plants make food: photosynthesis (Classes 6-8, Science)

  1. What does the word photosynthesis mean?
  2. Name the three things a plant needs for photosynthesis.
  3. What is the green substance in leaves called?
  4. Which gas do plants take in for photosynthesis?
  5. Which gas do plants give out during photosynthesis?
  6. What are the tiny holes on a leaf called?
  7. Which part of the plant takes in water from the soil?
  8. Write the word equation of photosynthesis.
  9. Count the oxygen atoms on each side of 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
  10. Why do plants matter for all food chains?

Part three

Answer keys

The answers to every practice sheet, in the same order as the lessons. Parents and teachers may like to keep these pages separately.

Answer key

Answers: Simple electric circuits

  1. Positive (+) and negative (−) terminals.
  2. A cell, wires, a bulb and a switch.
  3. No. An open switch leaves a gap, so the circuit is not complete and no current flows.
  4. A material that lets electric current pass through it, for example copper or iron.
  5. A material that does not let electric current pass through it, for example plastic or rubber.
  6. Copper.
  7. Plastic and rubber are insulators. They stop the current from passing to us and keep us safe.
  8. 1.5 V + 1.5 V = 3 V.
  9. The current can flow only if there is a complete path from one end of the cell to the other.
  10. Mains electricity is very strong and can cause serious injury or death.

Answer key

Answers: Light, shadows and reflection

  1. Any one of the Sun, a flame, a torch or a lit bulb.
  2. In straight lines.
  3. Transparent.
  4. Translucent.
  5. Opaque.
  6. The shadow becomes bigger.
  7. Reflection.
  8. 35°, because the angle of reflection equals the angle of incidence.
  9. 50° + 50° = 100°.
  10. A mirror swaps left and right, so a driver looking in the mirror reads the word correctly.

Answer key

Answers: Separating mixtures

  1. Hand-picking.
  2. Winnowing.
  3. Using a magnet.
  4. Heavy particles settling at the bottom of a liquid when it stands.
  5. Pouring off the clear liquid from the top without disturbing what settled at the bottom.
  6. A strainer (a kind of filter).
  7. Evaporation.
  8. Filtration.
  9. Dissolve the salt in water, filter to remove the sand, then evaporate the water to get the salt.
  10. It may still contain germs and dissolved impurities. It must be boiled or treated first.

Answer key

Answers: How plants make food: photosynthesis

  1. Making food using light.
  2. Sunlight, water and carbon dioxide (with chlorophyll in the leaf).
  3. Chlorophyll.
  4. Carbon dioxide.
  5. Oxygen.
  6. Stomata.
  7. The roots.
  8. Carbon dioxide + water → glucose + oxygen (in sunlight, with chlorophyll).
  9. Left: 6 × 2 + 6 × 1 = 18. Right: 6 + 6 × 2 = 18. Both sides have 18.
  10. Plants make food, so they are the producers on which all other living things depend.

The end

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