6. Time, Motion and Speed
9. Obtaining and Utilising Food
BASIC SCIENCE CLASS VII
HEAT: - it is a form of energy which produces a sensation of hotness or coldness . It is
measured in joules(J) or in calories. Heat energy flows from one body to another due to temperature difference between the two. Heat is an internal energy of the
substance due to molecular motion of the substance. www.rsmaths99.com
Q. State similarities and differences between the laboratory thermometer and the
1. Construction and working principal are same.
2. Both are used to measure temperature.
3. Both have a thick walled glass tube enclosing a fine uniform bore capillary tube.
4. Mercury is used in both thermometers to measure temperature.
5. Both have Celsius and Fahrenheit marking.
It is used to measure temperature of different objects in factories and laboratory.
For human beings only.
Temp. range from 10o – 110o c.
Range from 35o – 42o c.
Usually it does not have any constriction
It has the small constriction near the mercury bulb.
It has to be kept up right while taking the reading.
It can be tilted while taking reading.
đ No medium is required for transfer of heat by the process of radiation.
Q. Define temperature. What are the units used to measure temperature?
Ans. The degree of hotness or coldness is called temperature. It is measured in degree
Celsius (o c) Fahrenheit and Kelvin ( SI unit). www.rsmaths99.com
A Answer the following in not more than 20 words:
Q1 Give one example to show that heat is a form of energy.
Ans. When we heat a pan of water, the water boil at its temperature rises. The energy for this rise in temperature comes from heat. This shows that heat is a form of energy.
Q2. What is temperature? Name the scales used to measure it.
Ans. Temperature of a body is the measure of the hotness or coldness of the body,
Celsius and Fahrenheit are the scales used to measure temperature.
Q3. If the hotness or coldness of a body is relative, how do we measure its degree
Ans. We measuring the degree of hotness or coldness of a body by measuring its
Q4. Mention three changes that heat causes in substances. www.rsmaths99.com
Ans. Following are the three changes that heat can cause in any substance.
a) Heat can change the temperature of a substance.
b) Heat can expand a substance.
c) Heat can change the state of a substance.
Q5. A steel spoon dipped in a pot of boiling soup for a few minutes becomes to hot to
touch. How does heat travel through the spoon?
Ans. heat travel through the spoon by conduction.
Q6. How is it that we can hild a match while it is burning?
Ans. We can hold a match while it is burning as we hold only the wooden part of the
match stick. Wood is a bad conductor of heat and does not support transfer of heat through conduction, the remaining cold enough to be held easily in hand. While its other end is on fire. www.rsmaths99.com
Q7. Ans. Heat from the heater transfer to the whole room through radiation
Q8. Ans. Heat from the sun reaches the earth by the process of radiation.
Q9. Ans. Heat and light both are form of energy and both travel in a straight line.
Q10. Ans. The flow of heat from the hotter body to the colder body will stop when
temperature of the two bodies become equal.
Q1. Distinguish between the Celsius and Fahrenheit scales. www.rsmaths99.com
The melting point of ice is taken at 0o C.
The melting point of ice is taken at 32o F.
The boiling point of water is taken at 100o C.
The boiling point of water is taken at 212o F.
Q2. When a pan of water is heated on a gas stove, all the water turns hot in a while. How does heat travel through the water?
Ans. Convection is a process through which heat travels through the water. When a pan of water is heated, the water expands and become lighter. The hot water rises up and is replaced by the cooler water from the above. The cooler water is then heated. This process is repeated till all the water in the pan gets heated.
Q3. What happens to radient heat when it falls on a body? What does the absorption of radient heat by a body depend on?
Ans. when radiant energy falls on an object, some of its part is absorbed by the
object and some is reflected by the object. Absorption of the radiant energy depends upon the following:
1. The colour of the object.
2. Nature of the surface. www.rsmaths99.com
Q4. A] Mention one difference between the transfer of heat by conduction and
that by radiation.
It is a process by which heat travels through a medium without the movement of the material.
It is a process by which heat travels without the help of any material medium.
B] Mention one difference between the transfer of heat by conduction and that by
It is a process by which heat travels through a medium without the movement of the material.
It is a process by which heat travels through a medium by the movement of medium.
Q1. Explain how land and sea breezes originate. www.rsmaths99.com
Ans. In a day time land get heated faster than sea. So land is hotter than the sea
during the day. When air comes in contact with the land becomes hot and rises, and the cooler air above the sea moves towards the land to take its place. This movement of air from sea towards the land is called sea breeze. After sunset, the land cools faster than the sea. The air above the sea is warmer than the air above the land. Air above the sea rises and the cooler air above the land moves towards the sea. This is called a land breeze.
Q2. How would you demonstrate to a friend that gases expand when heated?
Ans. By the following experiment we can explain that the gases expand when
heated:-Take a balloon and a glass bottle. Fit the balloon to the mouth of a glass
bottle. Place the bottle in a pan of water and heat it. The balloon will get inflated as the air inside the bottle becomes warm and expands. Take the bottle out of the pan and allow it to cool. The balloon will get deflated as the air inside he bottle gets cooler. This experiment shows that the gas expands when it is heated.
Q3. Explain why
A] It is better to wear lighter shades in summer. www.rsmaths99.com
Ans. It is better to wear lighter shades in summer because light shades absorb less
B] Two thin sweaters feel warmer than one thick sweater.
Ans. Two thin sweaters feel warmer than one thick sweater because the air trapped
between the two sweaters act as an insulator of heat. It dose not allow the heat from our body to escape easiy.
C] Utensils are made of metal, while their handles are made of plastic.
Ans. Utensils are made of metal, while their handles are made of plastic because plastic is a bad conductor of heat. Therefore, heat does not flow easily to our hand. This saves our hand from the heat. Metal on the other is a good conductor of heat which allow heat from flame to the food easily. It helps in cooking fast.
6. TIME, MOTION AND SPEED
Q1. What is a unit of measurement?
Ans. A unit of measurement is a known fixed quantity with which we compare an unknown quantity we wish to measure.
Q2. Define speed and mention the SI unit of speed. www.rsmaths99.com
Ans. Distance travelled by a body in unit time is known as speed. SI unit of speed is meter per second. Speed(s) = distance travelled(d)/ time taken(t)
Q3. When is a body said to be in motion?
Ans. A body is said to be in motion if it position changes with time.
Q4. How are stopwatches different from ordinary watches?
Ans. Stopwatch has switch with which they can be started and stopped at will. They are used to measure time intervals during scientific experiments, sports events and so on.
Ordinary watches mark the passage of time continuously . It cannot be used to measure interval of time. www.rsmaths99.com
Q5. What property of a pendulum made it suitable to be used in the manufacture of clocks?
Ans. The motion of a pendulum is periodic means a swinging pendulum takes a fixed time to complete an oscillation (one to-and fro motion) . This property of a pendulum made it suitable to be used in the manufacture of clocks. The pendulum in such a clock takes a second to complete an oscillation.
Q6. What is the time period of a pendulum?
Ans. The time a pendulum takes to complete one oscillation is called its time period. The time period of the pendulum is the time the bob takes to move from A to B to c, and then back to A. (fig-6.3 in book).
Q7. Mention the factor that determines the time period of a pendulum.
Ans. It depends on the length of the pendulum.
Q8. When is a moving body said to be in uniform motion?
Ans. If a body moving along a straight line with a constant speed constant, or does not change with time is said to be in uniform motion. In this case, the average speed is the same as the actual speed.
Q9. Correct the following. www.rsmaths99.com
a] 90 m. = 90 m b] 100 Kgs = 100 Kg c] 10 secs = 10 s d] 50 kilos = 50 Kg
Q1. Speed(s) = Given, d = 15 Km, t = 20 min = =
S = = = = 22.5 Km/h
For speed in m/s:
D = 15 x 1000 m = 15000 m, t = 20 x 60 s = 120 s
S = = = 125 m/s.
Q2. Given D = 400 Km, speed = 50 Km/h, T = ?
We know, S = => 50 = = => T = 8 h
Q3. Given, speed = 40 km/h, t = 6 h, d = ?
We know that, s = => 40 = d = 40 x 6 = 240 Km.
Given, S = 2.5 m/s
i] Let D = 5 then, T =
ii] Let D = 10, then, T =
iii] Let D = 15, then, T =
ii] Let D = 20, then, T =
Q5. Time = 4s, Distance = 3 m, Speed = =
Q1. What do you need to apply across a bulb to cause a current to flow through it?
Ans. We need voltage to apply across a bulb to cause a current to flow through it.
Q2. Why does a bulb get warmer than the wires that connect it to a battery?
Ans. We know that the higher he resistance, the greater is the heat produced. The resistance of the filament of the bulb is higher than that of the wires. That’s why a bulb get warmer than the wires that connect it to a battery.
Q3. A magnetic needle get deflected when brought near a current-carrying conductor. What does this show? www.rsmaths99.com
Ans. We know that a current-carrying conductor behaves like a magnet. It attract or repels other magnet means it applies a force on a magnet that’s why a magnetic needle gets deflected when brought near a current-carrying conductor.
Q4. What happens when you place an iron nail in a current-carrying coil?
Ans. When we place an iron nail in a current-carrying coil the nail become a magnet.
Q5. Why do we use a soft iron core in an electromagnet?
Ans. We use soft iron core to make sure that an electromagnet loses its magnetism once the current is switched off. If steel or some other magnetic alloy were used for the core, it would retain magnetism even after the current was switched off. That’s why we use a soft iron core in an electromagnet.
Q6. Name four devices that use the heating effect of electric current.
Ans. The four devices that use the heating effect of electric current such as electric heater, irons, toasters, micro wave oven and OTG.
Q7. Mention four applications of electromagnets. www.rsmaths99.com
Ans. Four applications of electromagnets are as below-
i] It is used in cranes to pick up iron objects.
ii] it is used in electric doorbells, buzzers and telegraph, telephone etc
iii] In electric motors that drives fan, mixtures, washing machines etc.
iv] It is used in different type of machines in factories, and in large generators.
Q1. What is a circuit diagram? Draw the circuit diagram of a torch which works on three cells.
Ans. A circuit diagram is a representation of a circuit using standard symbols for its components.
Q2. Identify the following symbols. Also mark the positive and negative terminals in the symbol for the cell.
Ans. 1. Cell 2. Bulb 3. Battery 4. Switch(open) www.rsmaths99.com
Q3. How is the heat produced by an electric current related to resistance and the magnitude of the current?
Ans. Heat produced depends on two things first resistance and second magnitude of the current. The higher the resistance, the greater is the heat produced. Example – the resistance of the filament of the bulb is higher than that of the wires. That is why it becomes hotter. For a given resistance, the greater the current, the greater is the heat produced. Example- the wire has a low resistance, which allows a large current to flow in the circuit. This produces a large amount of heat, which makes the wire hot.
Q4. Why is a long and thin tungsten filament used in a bulb?
Ans. A long and thin tungsten filament used in a bulb because it has a higher resistance than ordinary wires. When a current passes through the filament, it gets heated and starts to glow. It has a very high melting point so it does not melt.
Q5. Mention two problems associated with the heating effect of electric current.
Ans. When an electric current flows through a conductor a part of the electric energy is converted into heat energy, this is a waste of energy. Second problem due to heat, it can damage the insulation on wire, damage electrical components or cause fires.
Q6. What is an electromagnet? Mention two properties of an electromagnet.
Ans. A magnet produced by passing an electric current through a coil wound around a soft iron core is called an electromagnet. Following are the two properties of an electromagnet:- www.rsmaths99.com
1. An electromagnet’s strength depends on the number of turns of wire and the amount of current passing through it.
2. An electromagnet is not a permanent magnet, once the current stops, the iron
core loses its magnetism.
Q1. What is electric resistance? On what does the resistance of a piece of material
depend? How does resistance affect current?
Ans. The electrical resistance of a piece of a material is a measure of the difficulty it creates to the flow of a electric current.
The resistance of a piece of material depends on the thickness and length of the material.
Resistance obstruct to the flow of electric current. The lower the resistance the greater is the current.
Q2. What is a fuse? How does it work? www.rsmaths99.com
Ans. A fuse is a safety device that opens an electric circuit when excessive current flows through it. A fuse has a special wire as the current increases very high the wire in the electric fuse melts and breaks the circuit and prevent any damage.
Note: opens an electric circuit (means disconnect the electric flow)
Q3. Explain with the help of a diagram the construction and working of an electric bell.
Ans. In an electric bell there are two switches connected to the electromagnet’s circuit. It consist of two parts S an T. When the outer switch is switched on the current flows through the electromagnet inside the bell and it pulls the hammer towards it. As soon as the hammer moves towards the electromagnet the circuit is broken from the terminal T, the electromagnet discharges and it again goes back to the terminal T. this process is repeated again and again frequently and the gong or hammer hits the bell. This produces the sound of the bell.
[fig in book] www.rsmaths99.com
[ Note: Resistance: the resistance(R) of an object is defined as the ratio of voltage across it(V) to current through it(I). R = V / I Resistance: Resistance is a hindrance or difficulty to the flow of current.]
Q1. What do you understand by the rectilinear propagation of light?
Ans. It is a property of light due to which light is travels in a straight line.
Q2. What is the relation between the incident ray, the reflected ray and the surface of a plane mirror? www.rsmaths99.com
Ans. The incident ray and the reflected ray make equal angles with a plane mirror.
Q3. Write three properties of the image formed by a plane mirror.
Ans. The image formed by a plane mirror is virtual and erect and its size is the same as that of the object.
Q4. An object is placed beyond the focus of a concave mirror. What is the nature of the image-real or virtual, erect or inversed?
Ans. If an object is placed beyond the focus of a concave mirror, the image formed is real and inverted.
Q5. An object is placed beyond the focus of a convex lens. What is the nature of the image-real or virtual, erect or inversed?
Ans. If an object is placed beyond the focus of a convex lens, the image formed real and inverted.
Q6. You have a concave mirror. Where will you place an object to see an erect and magnified image? www.rsmaths99.com
Ans. We will place an object closer to a concave mirror than the focus of the mirror to see an erect and magnified image.
Q7. You have a convex lens. Where will you place an object to see an erect and magnified image?
Ans. We will place an object between a convex lens and its focus to obtain an erect and magnified image.
Q8. Mention two uses of a concave mirror.
Ans. Two uses of a concave mirror are –
a] It is used as compact and shaving mirrors.
b] it is used to converge the sun light.
Q9. State two uses of a convex lens.
Ans. Two uses of a convex lens are –
a] it is used as rear-view mirrors
b] it is used in a magnifying glass.
Q10. What is white light?
Ans. white light is a mixture of seven colours and looks colourless.
Q1. Why is the image formed by a pinhole inverted? www.rsmaths99.com
Ans. When the rays from an object cross a pinhole, the rays from he top half of the object are below the rays from the bottom half. Their positions remain unchanged because light travels in straight lines. So, when they fall on a screen, the image formed is inverted.
Q2. What happens when parallel rays of light fall on a curved reflecting surface?
Ans. When parallel rays of light fall on a concave reflecting surface, the ray of light will meet(converge) at a point and when it reflect from the convex surface, the rays of light will seem to be coming from(diverging from) a point.
Q3. Convex mirrors are used as rear-view mirrors. Why?
Ans. The image formed by a convex mirror is always virtual, erect and smaller than the object. That is why Convex mirrors are used as rear-view mirrors.
Q4. What do you understand by the spectrum of white light?
Ans. The set of seven colour s formed on splitting of white light is called the spectrum of white light. These colours appears in the order violet, indigo, blue, green, yellow, orange and red. ( VIBGYOR).
Q5. How is rainbow formed? www.rsmaths99.com
Ans. when sunlight passes through raindrops at certain angles, it bends very sharply. This makes the separated colours visible and we can see as a rainbow in the sky.
Q6. Why does a Newton’s disc appear white when it is rotated?
Ans. When Newton’s disc is rotated, all the colour s passes through a spot rapidly one after other. This has the effect of putting all the colours in one place. This colour mix appears white.
Q1. What are the real and virtual images? What are the differences between them?
Ans. Real image:- An image that can be formed on a screen.
Virtual image:- An image that cannot be formed on a screen.
It can be formed on the screen
It cannot be formed on the screen
The rays of light after reflection meet at a point.
The rays of light after reflection appears to meet on a point.
It is always inverted.
It is always erect.
Q2. What do you understand by the focus of a lens? How will you find the focus of a convex lens?
Ans. The point where parallel rays of light actually meet or seem to come from after passing through a lens is called the focus(F) of the lens.
To find the focus of a convex lens, take a convex lens or a magnifying glass. Turned the lens towards the sun, slowly move it away from the ground. When the lens is at a certain distance from the ground we see a sharp image of the sun at a point.this is the point at which the parallel rays of the sun converge after passing through the lens. This point is called the focus of the lens.
Q3. What is refraction? Explain with an example. www.rsmaths99.com
Ans. The bending of light when it travels from one medium to another is called refraction of light. Eg.- When we put a spoon in a glass of water, the part of the spoon in water looks bent. This happens because light bends, or refracts at the surface separating two medium like water and air.
2. OBTAINING AND UTILISING FOOD
Q1. All living beings procure energy from food. Name the three life processes which help them do this.
Ans. (i) Nutrition (ii) Transportation (iii) Respiration
Q2. What are autotrophs? Name an organism other than green plants that is an autotroph. www.rsmaths99.com
Ans. Organism that make their own food from simple raw material are called autotrophs. An organism that is an autotroph is Algae.
Q3. Name the three types of heterotrophic nutrition.
Ans. The three types of hetrotriphic nutrition are –
Q4. What are enzymes?
Ans. Enzymes are special chemical substance produced in body of an organism. They help in the digestion of food. www.rsmaths99.com
Q5. Name the steps involved in the process of holozoic nutrition.
Ans. The steps involved in the process of holozoic nutrition are Ingestion, Digestion, Absorption, Assimilation, Egestion.
Q6. Name three things a green plant need in order to photosynthesise.
Ans. Water, carbon dioxide and sunlight are the three things a green plant need in order to photosynthesis.
Q7. What is the juice secreted by the liver called? What does it do?
Ans. The juice secreted by the liver is called Bile. Bile helps to break down fats into small droplets. This makes the digestion of fat easier. www.rsmaths99.com
Q8. Name a parasitic plant, and a parasite that lives in our intestine.
Ans. Dodder is a parasitic plant, and tapeworm is a parasite that lives in our intestine.
Q9. What is digestion?
Ans. Digestion is the process of breaking down food into simple, soluable molecules.
Q10. Name the holozoic animal that is not a herbivore, carnivore or omnivore.
Ans. Amoeba is a holozoic animal that is not a herbivore, carnivore or omnivore.
Q1. What are saprophytes and parasites?
Ans. Saprophytes: organism which feed on dead and decaying organic matter are called saprophytes. They break down the organic matter and it has a great importance to the environment. Ex.- yeast, fungi and bacteria.
Parasites: Parasites are organism that live inside or on another organism and draw nutrition from it. Ex.- tapeworms, hookworms and pinworms.
Q2. Write about two special features related to the teeth of a herbivore.
Ans. Two special features related to the teeth of a herbivore are :- 1. most of there teeth are on the sides of the jaws for chewing grass and green plants.2. their sharp-edged incisors are in front of the jaws for cutting grass .
Q3. Write briefly about the process of nutrition in the amoeba.
Ans. When an amoeba senses the food in its surroundings it sticks out fingerlike projections called pseudopodia and engulfs the food. This intake food form a food vacuole where amoeba digests it with the help of enzymes. www.rsmaths99.com
Q4. Why do carnivorous plants trap insects? Explain how one such plant traps insects.
Ans. They trap insects to get their supply of nitrogenous compound from which they make proteins. The leaves of the sundew, have hairs that secrete a sticky liquid which look likes dew. When insects, attracted by the glistening drops and sit on the hairs, the hairs bend over them and chock them.
Q5. What are symbionts? Explain with an example.
Ans. Symbionts are organism that live together for mutual benefit. For example, Lichens are symbionts consisting of a fungus and an algae that cooperate with each other to meet their food requirements. The fungus provides minerals and water to the alga. The alga supplies the fungus with food that it manufactures.
Q6. How did Dr. Beaumont study the functioning of the stomach?
Ans. Dr. Beaumont, while treating a patient St. Martin, who was accidently hit by a bullet in the stomach, he treated him 18 months, after that he found, a hole was left in stomach even though the wound had healed. When Dr, Beaumont experiment with the food from St. Martin’s stomach for nine years, he found that digestion of food occurs in the stomach due to the mixing of the juices with food.
Q7. What is the digestive juice in the mouth called? What enzyme does it contain and what does it do? www.rsmaths99.com
Ans. Digestive juice in the mouth called saliva. It contains the enzyme amylase. It acts on the starch present in the food like roti and rice and changes it into sugar.
Q8. What is peristalsis? Does it occur only in the oesophagus?
Ans. The series of contractions in the oesophagus to push down the food is called peristalsis. No, it occurs all the way down the alimentary canal.
Q9. The juice produced in the stomach contains an acid as well as an enzyme. Name the enzyme. What do the acid and enzyme do?
Ans. The juice produced in the stomach contains hydrochloric acid an enzyme called pepsin. When food comes in the stomach the digestive juice, which contains hydrochloric acid and an enzyme pepsin, the acid kills the germs and pepsin helps to break down proteins.
Q10. What happens to the undigested food that remains in the large intestine ?
Ans. The undigested food that remains in the large intestine some water is absorbed in the large intestine and the remaining semi-solid waste is egested through the anus.
Q1. How would you show that chlorophyll is needed for photosynthesis?
Ans. We will take a green leaf and put it into a test tube containing alcohol. Then we will heat it in a beaker containing water. We will leave it for sometime, when alcohol will turn green, we will take it out and wash it with warm water. Then we will put some Iodine solution over the leaf. We observe that the area where the leaf was green turns blue-black, this indicates the presence of starch and white parts of the leaf turns yellowish in colour. This shows that plants cannot manufacture food without chlorophyll. www.rsmaths99.com
Q2. What happens to food in the small intestine?
Ans. The main function of the small intestine is digestion and nutrients absorption. When partially digested food enters in the small intestine, pancreatic juice, bile from the liver and intestinal juice act upon food. Bile breaks down fat into small droplets. Digestion is completed in the small intestine. The inner wall of the small intestine has millions of fingerlike folds, called villi. The digested food which contains nutrients is passes through the villi and absorbed by the blood.
Q3. How many teeth does an adult ( human being) have? Describe the different types of teeth and their functions.
Ans. An adult has 32 teeth embedded in the upper and lower jaws. We have four different types of teeth they are: www.rsmaths99.com
i] Incisors: front teeth in a jaw are called incisor they are flat and bladelike. It helps in cutting food.
ii] Canines : either side of the incisors are called canines. They are pointed and help in tearing food. The no. of canine is 4 in all person.
iii] Premolars: next to the canine are called premolars. They are in 8 nos. These teeth are used for chew and grinding food.
iv] Molars: next to the premolar is called molars. There are 12 molars in all and they are larger than the premolars. It helps in grinding the food.
Q4. What is special about a ruminant’s stomach? How does it help the animal digest vegetable matter? www.rsmaths99.com
Ans. Ruminants have four-chambered stomach which help them digest cellulose. Ruminants chew partially the vegetable matter before swallowing it. Half-chewed vegetable matter travels from the mouth to the first chamber, where it acted upon by the bacteria. The half-digested food then enters in a second chamber, from where it is sent back to the mouth, to be chewed again. This re-chewing is called rumination. This food is swallowed again and goes to the third chamber. Here it is broken down into still smaller pieces and then finally, it enters the fourth chamber, where enzymes act upon it and digestion is completed.
1. proboscis 2. Absorption 3. Enzymes 4. Alimentary canal 5. Mouth
6. Villi www.rsmaths99.com