Electricity and circuits

1.Define electricity.

Ans Electricity is the flow of charges from positive terminal to the negative terminal.

2.What are the uses of electricity?

Ans 1. It is used to operate pumps to lift water from the well to tanks
2. It is used in the lighting of homes, streets, etc.
3. It is used in industries.
4. It is used in electric appliances.

3.Define an electric cell.

Ans Electric cell is a device that converts chemical energy to electrical energy. It has two terminals-

1. Positive terminal (metal cap is positive terminal)

2. Negative terminal (metal disk is negative terminal)

                                                 

The symbol of a cell is -    

  The symbol of a battery is -    

4. Define a battery.

Ans A battery is the combination of two or more cells.

5. Write the construction of an electric bulb.

Ans An electric bulb consist of a small glass cover fixed on metal case. Inside the glass cover there is a very thin wire fixed between two thick wires. The thin wire inside is called filament. Filament is usually made up of tungsten. It is the filament of the bulb which glows while electricity pass  through it. The two thick wires inside the glass bulb provides support to the filament and also makes the connection of the filament to the outer circuit. The lower end of one of the thick wires is connected to the metal tip at the bottom of the bulb. Whereas the lower end of the other thick wire is connected to the metals case. The metal tip of the bulb at the base and the metal case of the bulb are the two terminal of the bulb.

6. What is an electric circuit?
Ans The complete path of electricity between the two terminals of an electric cell is called and electric cell.

   

the symbol for bulb is

7. What are the different types of circuits?
Ans Electric circuits are of two types-1.Open circuit- when there is a breakage in the path of electricity is called an open circuit.2.Closed circuit- when there is no breakage in the path of electricity is called a closed circuit.

                      

8. What are the properties of a filament?
Ans The properties of a filament are-1. It has high resistance for electric current.2. It has high melting point.3. They don't get oxidized even at high temperature.

9. What is an electric switch ?
Ans Electric switch is an electric device which make or break a circuit. If it makes a circuit then it is switched on and if it breaks a circuit it is switched of.

10. Define-
a) Conductor- Substances that allow electricity to pass through them are called conductors of electricity. eg metal , our body, etc.
b) Insulator- Substances that don't allow electricity to pass through them are called insulators of electricity . eg pure water, diamond , wood , etc.

11. Why should an electrician use rubber gloves while preparing an electric switch at home?
Ans Our body is a good conductor of electricity and rubber is an insulator of electricity. During repairing work, if our body comes in contact to a wire carrying electricity , there will not be any accident as rubber doesn't allow the passage of current through it. Hence, electrician use rubber glows while repairing a switch.

12.The handles of tools like screw drivers, pliers, etc are made of plastic or rubber handles. Explain?
Ans Plastic and rubber are insulators of electricity. When these tools come in contact with current carrying wires. Due to plastic or rubber handle any accident don't occur.

13. Who invented electric bulb and electric cell?
Ans Thomas Alva Edison is the inventor of the electric bulb.
Alessandro Volta is the inventor of the electric cell.

14. What are the advantages of an electric cell.
Ans 1. Electric cell are light so they are portable 2. They produce very small amount of electricity so they are perfectly safe. So one can handle them without receiving an electric shock.3. They are not very costly.4. They don't contain any liquid chemicals that can be spilled.5. They supply a steady electric current.

        An electric cell



15. Why do bulbs have two terminals?
Ans Bulbs have two terminals to connect the filament with circuit so that current can easily pass through.

16. A fused bulb doesn't glow. Why?
Ans The circuit in a fused bulb is incomplete due to breaking of filament. thus, the fused bulb does no glow.

17. Rita wanted to glow a torch bulb using a cell she could not get connecting wires instead she used two stripes of aluminium foil. Will she succeed. How ?
Ans Aluminium foil is a good conductor of electricity so they can be used as connecting wires.

18.Write the preventive measures to avoid electric shock.
Ans 1.Replace the light bulb only when it is switched of and cool.2. Never touch electric switches or gadgets when your body is wet.3. Don't try to repair or install electrical wiring or appliances.4. Don't touch electric poses or transformers on the road.5. Don't touch a hanging wire on the road.6. Never fly kites near overhead power lines.7. Never join the electric wires with bare hands.

19. We remove the plastic coating from the ends of the electric wires while using in an electric circuit. Why ?
Ans It is because plastic is an insulator of electricity. We remove the plastic covering to connect the copper wires so that electric current can pass.

inside of a torch

            

  Changes Around Us

1. How do you know that a change has taken place?

Ans We can know that a change has taken place if there is a change in color, odor, position, new substance is made etc.

2. What are the factors that cause a change? 

Ans The factors that cause a change are-

1. passing light and electricity

2. by changing temperature 

3. by applying force

4. by mixing two substance.

3. Write differences between physical changes and chemical change.

Ans Physical change -

1. The change of shape, size, position, state of matter are called physical change.

2. They are temporary.

3. Some of them are reversible.

4.New substance is not formed

Chemical change-

1. The change when a new substance is formed is called chemical change.

2. They are permanent.

3. They are not reversible

4.Write four examples each of physical and chemical change.
Ans Physical change- cutting fruits, stretching a rubber band, melting of ice, melting of wax
Chemical change- rusting of iron, burning of paper, boiling of an egg, frying and egg.

5. Write 10 examples of Reversible and Irreversible changes.
Ans Reversible change- stretching a rubber band, folding a paper, modeling clay, inflating a balloon, drawing a line with a pencil, bending of straw, opening a plastic lid, melting of ice, evaporation of water, water into ice.
Irreversible change- growth of a child, aging, baking a cake, cutting of vegetable,breaking a chair, slicing a bread, burning of paper, curdling of milk, breaking a glass , breaking a magnet

6. Define reversible and irreversible change.
Ans Reversible change- changes that can be reversed by reversing the cause to get the original substance is called a reversible change. eg inflating a balloon, etc
Irreversible change- Changes that can't be reversed by reversing the cause to get the original substance is called and irreversible change. eg rusting of iron.

7. Define physical change and chemical change.
Ans Physical change- A change in which a substance undergoes a change in its physical properties is called physical change.

Chemical change-A change in which one or more new substance are formed is called chemical change.

8. Write some examples of changes caused by heating.
Ans The changes caused by heating are-
1.Some objects get simply heated but no other changes take place.
2.Some objects expand on heating.
3.Some objects burn on heating.
4.Some objects change their state.

9. Classify the following changes into physical and chemical changes-
a) Melting of was- melting of wax is a physical change as there is a change in state and shape which is a physical properties.
b) Burning of paper – burning of paper is a chemical change as a new substance is formed (ash) and the original substance cannot be retained.

10. How does a blacksmith change a piece of iron into different tools?
Ans A blacksmith first heats a piece of iron till it becomes red hot. Then it becomes soft and can be beaten into desired shape.

11. How is a wooden handle fixed to an iron tool?
Ans The iron blade of the tools has a ring to which the wooden handle is fixed. Normally the ring is slightly smaller than the wooden handle. To fix the handle, the ring is heated and it expands, now the handle easily fix to the ring. When the ring cools down it contracts and fix tightly to the handle.

12. How is a metal ring fixed on a wooden wheel of a cart?
Ans The metal ring is made slightly smaller than the wheel. On heating the ring expands and fixed on the wheel. Cold water is then poured over the rim, which contracts and fits tightly to the wheel.

13. Why is the shaping of wet clay into a clay pot a reversible change, whereas baking a clay pot is irreversible change?
Ans The shaping of wet clay into a clay pot is a reversible change because it can be change to wet clay (get the original substance back) . And baking of a clay pot is irreversible as the pot cannot be changed to wet clay.

14. You must have seen that construction workers heat a black thing called Coal Tar to repair roads. State whether the heating of coal tar is reversible or irreversible.
Ans When coal tar is heated it melts to form a thick dark liquid (change of state). Melting of coal tar is a reversible change as it solidifies on cooling.

15. When water is mixed with plaster of Paris and allowed to dry. It sets into a hard mass. State whether it is reversible or irreversible.
Ans This is an irreversible change as when water is added to Plaster of Paris it sets to its hard form and can't be converted back.

Motion and Measurement of distances

1.What do you mean by rest and motion?
Ans  A body is said to be at rest when it doesn't change its position with respect to its surrounding object.
eg a rope lying on the floor. A body is said to be at motion when it changes its position with respect to its surrounding. eg a moving car.

2. What is the need of measurement. What are standard units and why are they important?
Ans  It is difficult to make correct judgement without making actual measurement. Therefore to make your judgement more reliable and accurate actual measurements are taken.
 The unit which is acceptable to the majority of the people as a basic unit of measurement is called a standard unit for the people.
 For uniformity and convenience a common unit is necessary for a measurement of a physical quantity.

3.  What is measurement and unit?
Ans Measurement is the comparison of an unknown quantity with a known fixed quantity of the same kind.
 The known fixed quantity is called unit.

4. What do you mean by International System of units (SI)?
Ans Scientists all over the world have accepted a basic set of units for the measurement of physical quantity(SI).
According to the system of SI unit of length is metre (m) mass in kilogram (kg) time is seconds (s) and temperature is Kelvin (K).

The distance between the tip of the middle finger and elbow is Cubit.
The distance between the tip of the thump and little finger is Hand span.
Distance between the feet is called Pace. 

The commonly used units of length are- cm, m, mm, km, etc.

5. Raju and Kevin live 2000 m away from each other. Express the distance between them in km.

Ans 2000 m = 2km

length is measured by a ruler, measuring rod, etc. 

odometer is a device used to measure distance covered by a vehicle.

mass is a quantity of matter contained in an object. It is measured in kg in SI units.

The devices used to measure mass are spring balance, beam balance, electronic balance, etc.

Time is measured in sec in SI units using clock, wrist watch, etc.
Temperature is measure of coldness or hotness.
It is measured by thermometer.

6. List the precautions that one should take while measuring length with a ruler.
Ans We should take the following precautions while measuring length with a ruler -
1. Care should be taken to keep the ruler along the objects.
2. Eye should be exactly above the pint where the measurement has to be taken.
3. If the edge of the ruler is worn out or broken the measurement should be taken from any other mark, that is fully clear and then subtract the final measurement by that number.

7. How can we measure the diameter of a ball or a coin?
Ans To measure the diameter of a ball or coin we should use two wooden blocks. Place the ball or coin on a table and place the blocks such that both the blocks touch the ball. Now keep a ruler near the lower edges of the wooden blocks. Now measure the distance between the faces touching the ball. This is the diameter. 

8. Write the different types of motion?
Ans 1. Translatory motion- When all parts of an object move the same distance at the same time. then the object is said to be in translatory motion.
It is of two kinds-
a) Rectilinear motion- When all the parts of an object cover the same distance along a straight line in a given time. It is said to be in rectilinear motion. 
eg a train moving in a straight track, etc
b) Curvilinear motion- When an object moves around a curve line is called curvilinear motion. 
eg a car moving in a curve road, etc.

2. Circular motion- When an object moves in a circular path around a fixed path and point it is said to be in circular motion.
It is of two types-
a) Rotational- When a body moves about a fixed axis without changing its motion It is said to be at rotational motion. 
eg blades of a moving fan, etc.
b) Revolution- When the objects change its position when it moves in a circular path is said to be at revolution.
eg revolution of Earth 

3.Periodic motion- The motion which repeats itself after some interval of time is called periodic motion. 
eg heartbeat, pendulum of a clock, etc.

4. Non-Periodic motion- A motion that doesn't repeat itself in an interval of time is called non-periodic motion.
eg movement of a child, ducks waddling in water, etc.

5. Oscillatory motion- When a body moves to and fro about its mean position is called an oscillatory motion. eg pendulum of a clock, strings of a guitar.

6. Simultaneous motion- When an object undergo a combination of different types of motion then the body is said to be at simultaneous motion.
eg motion of Earth, wheels of a cycle, a ball rolling in a straight way.

9. What are the disadvantages of conventional methods of measurement?
Ans In conventional methods of measurement we use different body parts (cubit, hand span, etc) They are not reliable as they don't give accurate measurement as it varies from person to person.

 Light, Shadows and Reflections

1. What is light?

Ans Light is a source of energy that enables us to see things around us.

Sources of Light 

                                           Natural sources                  Man made sources

                                 Sun, Stars, fireflies, etc.              bulb, torch, etc 

Luminous bodies- bodies that emit their own light are called luminous bodies. eg Sun

Non Luminous bodies- bodies that don't emit their own light but reflects light that falls on it is called non luminous bodies. eg Moon, chair, table.

Moon is a natural non-luminous body which doesn't have light of its own but reflects the light of the Sun.

Light travels in a straight line. When we want to represent the propagation of light, we draw a ray.

When a group of rays moving in an organised manner it is called a beam of light.

2. What is Rectilinear propagation of light?

Ans The property of light to travel in a straight line is called Rectilinear propagation of light.

3. Write an activity to prove that light travels in a straight line.

Ans Aim - To prove that light travels in a straight line 

Materials required- 2 ft long rubber tube, candle, matchbox, plastic tube.

Procedure- Take a hollow plastic tube which can be bend easily. Light a candle and put it on a stand at a distance of 3 ft away from you. Observe the candle flame through the hollow tube. Now bend the tube and again try to see through it.

Observation- We will not be able to see when the tube is bend as light can't travel a curved path it can travel in a straight line. 

Conclusion-  The activity is proving that light travels in a straight line.

Transparent, Translucent and Opaque materials

Based on the amount of light that can pass through the materials. They are divided into-

1. Transparent materials

2.Translucent materials

3. Opaque materials

Transparent materials

Materials that allow light to pass through it is called transparent materials. We can see through it clearly. eg glass, plastic cover, etc

Translucent materials

Materials that allow little light to pass through it is called translucent materials. We can see through it but the image won't be clear. eg butter paper, muddy water, etc

Opaque materials

Materials that don't allow light to pass through it is called opaque materials. We cannot see through it. eg cardboard, brick, etc.

Refection of light

When a ray of light falls on a smooth polished surface, it bounces back. This is known as reflection of light. the bouncing back of light results in the formation of an image.

Plain Mirror
It is a thin, flat, smooth sheet of glass having a shiny coating of silver coating and paint.     
   

4.give any four phenomena that suggest that light travels in a straight line.
Ans 1.Formation of shadow.
2. A beam of light from the projector.
3. The headlight of a car when it is switched on.
4. When ray of light enter a dark room.

5. What is a pin hole camera?
Ans A pin hole camera works on the principle of rectilinear propagation of light. It demonstrates how light forms images of objects.

6. What are the properties of an image formed in a pin hole camera?
Ans 1.The image formed in a pin hole camera is inverted.
2. Diminished and details of the image such as colour, etc are clear in the image.

7. Why are the surfaces of a pin hole camera black?
Ans A black surface absorbs light rays thus, any extra light enters from the sides is absorb by it. This helps as to see the image clearly. If we don't paint the sides black, the image may appear or maybe dull.

8. What is a shadow? Mention the conditions required to form a shadow.
Ans A dark patch formed behind an opaque body when it is places in the path of light is called a shadow.
There must be a -
1. Source of light
2. An opaque object
3. An opaque screen to form a shadow.

9. How is an image formed in a pin hole camera?
Ans Luminous objects emit light in all directions. for example take two points P and Q that is the top of the candle and the base of the candle. A ray of light starting from point P will pass through the pin hole and meet the screen at P1, another ray of light starting from point Q will pass through the pin hole camera and meet the screen at Q1. The ray starting from different points between P and Q will meet he screen in between P1 and Q1 and thus form an inverted image of the object. Pin hole camera works on the principle of rectilinear propagation of light.

10 What will happen if the pin hole of the pin hole camera becomes bigger?

Ans If the pin hole of the pin hole camera becomes bigger one ray of light from the given point will enter the pin hole camera. This will result in a an overlapping of the image and a blurred image will be formed.

11. Define a mirror?

Ans A mirror is a smooth polished surface when light falls on it the light bounces back.

12. Differentiate between a shadow and an image formed in a pin hole camera?

Ans Shadow

Shadow is a dark outline formed behind an opaque body. No colours are seen in a shadow except black. They are not inverted . Shadows of an object can be misleading sometimes. Shadows can be smaller or bigger than the object.

Image in a pin hole camera

Image in the pin hole camera shows all the details of the object. All colours are seen in the image of the pin hole camera. Image formed in a pin hole camera is inverted. Image is not misleading. Image is always smaller than the object.

Lateral inversion

The left side of the object appears the right side of the image. This left-right reversal of an object and its mirror image is called lateral inversion.

Real image and Virtual image

Real image- An image that can be obtained on a screen is called real image. It is always inverted.  Eg image formed in a pin hole camera

Virtual image- An image that cannot be obtained from the screen is called virtual image. It is always erect. Eg image formed in a plane mirror

13. What happens to the size of a shadow when an object moves towards the source of light and away form the screen.

Ans The size of the shadow increases.

14. what happens to the size of a shadow when an object moves away form the source of light and towards the screen.

Ans The size of the shadow decreases

Body Movements

Questions and Answers.

1. What is the skeletal system?

Ans It is the framework of bones which protects and encloses the internal organs and give shape, strength and support to the body.

2. Which are the different types of bones in the skeletal system.

Ans there are 4 types of bones which are-

1. The Skull

2. The Spine

3. The Rib Cage

4. The Limbs (hind and fore limbs)

3. Explain the structure of the skull.

Ans The skull consist of 29 bones. It protects the brain and sensory organs.

Our of 29 bones -

8 are interlocked together and flat.

14 are facial bones enclosing the sensory organs.

6 are ear bones (3 in each ear)

1 in the neck (hyoid bone)

4. Explain the structure of Rib Cage.
Ans There are 12 pairs of ribs in a rib cage. 1-7 pairs are called true ribs. as they are connected to both backbone and the sternum. 8-10 pairs are called False ribs as they are connected to the backbone and 7th pair of rib. 11,12 are called floating ribs as they are only connected to the backbone and not the sternum. It protects the heart and the lungs.

5.Explain the structure of limbs (Forelimbs (arms) and Hind limbs (legs).
Ans Forelimbs- Forelimbs are joined to the shoulder girdle with the ball and socket joint. A Forelimb consist of Humerus, Radius, Ulna, carpals, Metacarpals and Phalanges.

Hind limb
A hind limb consist of Tibia, Fibula, Patella, Tarsals, Metatarsals and Phalanges. Hind limb is joined to the pelvis with a ball and socket joint.

7. What are the function of the skeletal system.
Ans It supports the body and gives definite shape and strength to it.
2. It helps to protect delicate and vital organs like heart, lungs and brain, etc.
3. With the help of muscles it helps in the movement of body parts.
4. It is the storehouse of minerals and the place of formation of Red Blood Cells and White Blood Cells.

8. What are vertebrates and invertebrates?
Ans Vertebrates
Animals which possess a backbone are called vertebrates. eg Human beings, monkey, etc.
Invertebrates
Animals which don't possess a vertebral column are called In vertebrates. eg Earthworm, spider, starfish, etc.

Skeletal system- Axial skeletal system( Spine, Rib cage, Skull) , Appendicular skeletal system( Forelimb, Hind limb, hip and shoulder Girdles)

9. Explain the structure of girdles.
Ans Girdles give support to the bones of the limbs. The Girdle that support the bones of the arm is called shoulder girdle. The shoulder girdle consist of two pairs of bones- One pair of clavicles (collar bone) and one pair of scapulae ( shoulder blade). the girdle into which bones of legs are fitted is called hip girdle (pelvis).

There are 3 bones in the middle ear they are incus, stapes ( smallest bone in the body) and malleus. 

Joints
A joint is a place where two or more bones meet. Bones are held together at a joint by a tissue called ligament. the ends of bones are covered with elastic, soft and flexible tissue called cartilage. It act as a shock absorber by preventing bones from rubbing against each other. A fluid called synovial fluid is also present between the joints to lubricate them.

Types of joint
On the bases of the movements joints are of 4 types-

Ball and socket joint
In this type of joint the ball like surface of one boll fits into a cup like hollow socket of another bone. this type of joint allow maximum movement. eg Joints present in the hip and shoulder girdle.

Pivot Joint
This joint the pointed part of one bone fits into the cavity of one bone that is the rounded surface of one bone fits into a ring form such that one bone is able to rotate over the other. Eg Neck joint

Hinge joint
This joint allows back and forth movement similar to the hinges of a door. Eg joints in the knee, finger, elbow and toes.

Gliding Joint
This kind of joint allows bones to glide over each other by providing a sliding movement in all direction. eg Joints in the wrist and spine 

Dislocation
Sometimes because of careless movement or a bad fall. the bones at the joint slip out of their position this is called dislocation of bones a person who has a dislocated bone may have sprain or damaged ligament.

Muscles
Muscles are attached to bones by a fibre like tissue called tendons. Joints cannot bring about a movement with out he help  of bones or muscle.One muscle pulls the bone away from the joint by contracting while the other muscle pulls it back by expanding. Biceps and triceps contract and expand respectively to move our forearm.

Movement in animals

Earthworm
Body of an earthworm is made up of number of segments. Its body is elongated, segmented and doesn’t have bones. It lives in moist soil, water and burrows. It respire through its moist skin. On the lower surface of its body hair like structure called bristle are present. These help it to get grip on the surface or ground when it moves.



10 How do earthworm help us?
Ans Earthworms live in the soil feeding on it. The undigested food is passed out as pallets while earthworms carry on their lives, like this they bring up the fertile soil from the bottom to the upper surface.
2. The earthworm make the soil soft and allow more air to get in. This helps the crops to grow healthier hence, we called them as ‘friends of farmers.’
3.The earthworm help in the decomposition of organic waste by converting it into useful fertilizes for the crop and plants.

Movement in earthworm
An earthworm can move in the soil by repeated contraction and expansion of muscles. Its body secretes a slimy substance that help in the movement. When an earthworm moves, the front end becomes long and thin and the rear end becomes short and thick due to the contraction and expansion of muscles.

Movement in bird
The features that help a bird to fly are-
1. Streamline body shape which reduces air resistance.
2. Hollow bones which makes them light weight.
3. They have wings made up of feathers.
4. They have very strong chest muscles and have large lungs.








Movement in a fish
They have streamline body shape.
Shape of the body reduces water resistance.
Fins play a major role in swimming.

The body of the fish is adapted for swimming in water in the following ways-
1. Streamline, spindle- shape body covered with scale. This body structure offers the least resistance and make their swim easier.
2. Skeleton is made up of thin bones with flexible backbone that help in swimming.
3. The swim bladder is filled with air to make the body buoyant making them to move up and down in water.
4. During swimming the front part of body curves on one side and tail on the opposite side than quickly it turns to its opposite side. This provide a jerk and pushes forward it repeats this for movement in forward direction. The body is balanced and kept steady by paired and unpaired fins.









Locomotion in snakes
The body of a snake is cylindrical, long and with scales. The scales on back are small. On ventral side the scales are big. The body has numerous muscles and vertebrae. The muscles interconnect the vertebrae, ribs and skin. They are also connected by tendons. Snakes slither on land to move by drawing on their belly. They form loops while moving. The forward push of the loops against the surface helps the snakes to move forward.

Movement in a snail

Its body is soft and unsegmented and it has a shell on its body. They have a pair of eyes and a pair of tentacles. It fells its foods with tentacles. They move slowly with the help of its flat muscular foot which produce a mucus. The snail crawls smoothly on the layer of mucus. The flat muscular foot is present under its belly when a snail moves. It looks like it’s moving on its belly.

Movement in a cockroach

The body of a cockroach is divided into head, thorax and abdomen. It has tree pairs of legs and two pairs of wings. Wings are attached to the breast muscles. The legs help them to crawl and climb. The wings help them to fly.

11. Fins play a major role in swimming in fish. Explain.

Ans 1. The Dorsal, pelvic and anal fins help the fish to balance its body in water and don’t allow it to topple.

2. The pectoral fins allow it to stop suddenly or to move slowly in water. These fins are like oars to push the water.

3. The tail of a fish acts like a rudder of a boat and helps it to change the direction of movement.