GRADE:-6 PHYSICS
Chapter-5 PRESSURE
• Answer the following in a word or two or in a sentence.
1. What is the SI unit of pressure?
Ans: Pascal
2. How are force, area of application of force and pressure related to each other?
Ans: Pressure = Force/Area
3. How is pressure effected if the force applied is doubled for the same area?
Ans: If the force applied is doubled for the same area, pressure is doubled.
• Answer the following in short :
1. Why do safety pins & drawing pins have narrow & sharp tips?
Ans: Safety pins & drawing pins have narrow & sharp tips because the smaller surface area of the tip causes a
high pressure and therefore, makes it easier for these objects to pierce through a given material.
2. Why do school bags have broad straps?
Ans: School bags have broad straps to reduce the pressure on our shoulders.
3. List any two application of pressure.
Ans: Knives, blades, scissor, high-rise building, caterpillar tracks in army tanks, wooden sleepers in railway
track.
• Answer in detail :
1. Define pressure. Write the factors on which the pressure exerted by a body depends.
Ans: Pressure is defined as the amount of force acting per unit area.
The factors on which the pressure exerted by a body depends are force and area.
2. What will be the effect of pressure on a body if the force applied on it becomes twice assuming that
there is no change in area?
Ans: If the force applied on a body becomes twice assuming that there is no change in area, then pressure
will be twice.
3. Where is pressure greater: 5 m below the surface of the sea or 10 m below the surface of the sea?
Ans: The pressure is greater at 10 m because the deeper we go under the sea, greater is the pressure of
water.
4. Why do the pillars of a bridge have a broad base & a narrow top?
Ans: The pillars of a bridge have a broad base & a narrow top to reduce the pressure exerted on the ground
by the enormous weight of the bridge.
5. How do high-rise buildings manage their pressure on the ground?
Ans: High-rise buildings have massive weight & thus apply large force on ground. Therefore, to reduce
pressure on ground they have a broad base.
• Numericals :
1. A box having a weight of 240 N is placed on a floor. If the area of its base is 8 m2, calculate the
pressure exerted by the box on the floor.
Ans: Given: F = 240 N, A = 8 m2
P = F ÷ A = 240/8 = 30 Pa.
2. The tip of a drawing pin has an area of 0.01 mm2. Find the pressure exerted by it if a force of 20 N is
applied on it.
Ans: Given: F = 20 N, A = 0.01 mm2 = 0.01 × 10-3 m2 = 10-5 m2
P = F ÷ A = 20 ÷ 10-5 = 2×106 Pa.
3. A motorcycle weighs 1200 N. If the pressure exerted by one of its tyres is 120 Pa, and then find the
area of the tyre in contact with the road.
Ans: Given: F = 1200 N,
Pressure exerted by 1 tyre = 120 Pa
∴ Pressure excited by 2 tyre = 120 × 2 = 240 Pa
P=F÷A
∴ A = F ÷ P = 1200 ÷ 240 = 5 m2.
4. A woman stands on high heels concentrating her weight on the tip of the heels. Calculate the pressure
excited by her heels on the ground if the area of contact of each heel is 2 cm2 & the weight of the
woman in 650 N.
Ans: Given: F = 650 N
Area of contact of each heel = 2cm2
∴ Area of contact of 2 heels = 2 × 2 cm2= 4 cm2 = 4/104 m2
P = F/A = 650/4×10-4 = 650×104 /4= 6500×103 /4 = 1625×103 Pa.
5. A swimming pool of width 8 m & length 36 m is filled with water to a certain height. If the pressure
exerted by the water on the bottom of the pool is 30,420 Pa, then find the force acting on the bottom
of the pool.
Ans: Given: P = 30,420 Pa, A = 8 m × 36 m = 288 m2
P = F/A ∴ 30,420 = F/288
∴ F = 30,420 × 288 = 87, 60, 960 N.
Chapter-6 WORK & ENERGY
• Answer in a word or two or in a sentence:
1. What will be the work done by a force acting on a body if displacement of the body is zero?
Ans: The work done by force acting on a body if displacement of the body is zero will be zero.
2. Give an example in which electrical energy gets converted to sound energy?
Ans: Door bell, head speaker.
3. Name the energy possessed by a flowerpot placed at the rooftop of a building.
Ans: The energy possessed by a flowerpot placed at the rooftop of a building is gravitational potential energy.
4. Name the energy transformation that takes place in a dry cell.
Ans: The energy transformation that takes place in a dry cell is chemical energy to electrical energy.
5. Give a method by which we can save energy.
Ans: We can save energy by using CFL bulb, LED bulb and solar products.
• Answer in short :
1. State the factors responsible for work done by a body.
Ans: The factors responsible for work done by a body are force & displacement.
2. Define kinetic energy & give an example of a body possessing kinetic energy.
Ans: The energy possessed by a body due to its motion or movement is called kinetic Energy.
Example: Running car, moving swing.
3. How do we get electricity from wind?
Ans: Wind possesses kinetic energy which is used to rotate the shafts of generator to generate electricity.
4. What are renewable sources of energy? Give 2 examples.
Ans: Sources of energy that do not get depleted on use & can be used again & again are called renewable
sources of energy.
Example: Sun, wind and water.
• Answer in detail :
1. What is meant by mechanical energy? Explain in detail.
Ans: The energy possessed by a body due to the work done on it is known as mechanical energy.
Work is done on a body when the body is displaced. So, the energy gained by a body due to its state of
motion, or due to its position is known as mechanical energy.
It is of 2 types :
1) Kinetic energy
2) Potential energy
2. Give reason why water stored in dam has potential energy.
Ans: Water stored in dam has potential energy because water in a dam has position & hence its energy is
stored in the form of gravitational potential energy.
P.E. = mgh
Where, m = mass, g = gravitational acceleration, h= height
3. Define an energy chain. Discus the various energy transformations that take place during a water
cycle.
Ans: Sun is the primary & the ultimate source of energy on our planet. Most of the phenomena taking place
around us involve more than one energy transformation or a series of energy transformations. Such series of
energy transformation are called energy chain.
The heat energy from the sun is responsible for evaporation of water from various water bodies. After
evaporation, this water forms clouds & clouds bring rains. This process is called the water cycle. The
mechanical energy of rain water has been caused due to solar energy.
4. Describe the work-energy relationship by giving a suitable example.
Ans: When an object is at a height from the ground, it has certain amount of potential energy. When we drop
the object, it falls down because of force of gravity. So, work is being done on the body. While falling down
its kinetic energy is used up until it becomes zero. At any point during its fall, the amount of kinetic energy
which is used up by the body is equal to the distance, the body has travelled.
Amount of work done by a body = Amount of energy change in the body.
• Numericals :
1. Find out the work done when a force of 80 N displaces a body through 5 m.
Ans: Work = Force × displacement = 80 × 5 = 400 Nm or J.
2. Calculate the work done in pushing a cart through a distance of 10 m against the force of friction
which is equal to 120 N.
Ans: Work = Force × displacement = 120 × 10 = 1200 Nm or J.
3. If 1000 J of work is done by a machine to move a body through a distance of 20 m, then find the force
applied on the body.
Ans: W = F × d ∴ 1000 = F × 20 ∴F = 1000 ÷ 20 = 50 N.
4. A boy applies a force of 25 N to push a box. Calculate the displacement of the box if the total work
done is 225 J.
Ans: W = F × d ∴225 = 25 × d ∴d = 225 ÷ 25 = 45 ÷ 5 = 9m.
Chapter-7 SIMPLE MACHINES
• Answer the following in a word or two or in a sentence.
1. Give an example of a class-I lever.
Ans: Examples of a class-I lever are pairs of scissors, pliers, wire cutters, beam balance, crow–bar and seesaw.
2. Which type of machine is used to squeeze a lemon?
Ans: Class-II lever is used to squeeze a lemon.
3. Write the relationship between mechanical advantage, load & effort.
Ans: Mechanical advantage = Load ÷ Effort.
4. Name the type of machine made by putting two inclined planes together.
Ans: Wedge is made by putting two inclined planes together.
5. Give one example of a machine used to multiply speed.
Ans: Wheel–axle arrangement is used to multiply speed.
6. Write the formula for calculation the efficiency of a machine.
Ans: Efficiency = Output energy ÷ Input energy.
• Answer the following in short :
1. State the various functions that a machine can perform.
Ans: The various functions that a machine can perform are
Changing the direction of applied force.
Changing the magnitude of applied force.
Applying force at a convenient point.
Changing the speed of an object.
2. What is the basis of classification of levers?
Ans: Load, fulcrum & effort are the basis of classification of levers.
3. What is the function of a screw? Give any one use of a screw.
Ans: The function of a screw is to convert rotational motion into linear motion.
Example: Nut & Bolt.
4. Using a suitable example, describe how a machine acts as a force multiplier.
An inclined plane is used to lift a heavy box.
Mechanical advantage of inclined plane = Length of plank ÷ vertical height of load raised.
As mechanical advantage of inclined plane is always greater than 1. Therefore, it acts as a force
multiplies.
5. What do you understand by the term efficiency of a machine?
Ans: Ratio of work done by the machine to the work done on the machine is termed as efficiency of a
machine.
6. Mention any 2 methods by which we can take care of machines.
Ans: We can take care of machines by keeping in clean environment, preventing from dust, preventing from
rust, regularly oiled.
• Answer the following in detail :
1. Draw simplified diagram by clearly showing the position of load, effort & fulcrum for class I, class II &
class III levers.
Ans: For class I lever, class II lever and class III lever: Refer figure from textbook.
2. How does a pulley make work simpler? Differentiate between a single fixed pulley & a single movable
pulley.
Ans: A pulley is used to lift heavy objects. A rope or a metal chain passes through the groove which prevents
the rope from slipping off the disc. The load to be lifted is attached to one end of the rope, whereas the
effort is applied at the other end.
Single fixed pulley
Single movable pulley
1. It has a fixed axis of rotation.
Its axis of rotation is not fixed.
2. Pulley is attached to high platform.
Load is attached to the pulley.
3. One end of rope is attached to load.
One end of rope is tied to the lower surface of a
platform
3. Explain the wheel & axle arrangement in brief.
Ans: It consists of 2 cylinders of different diameters joined together such that if one is made to rotate, other
also rotates. Axle is fixed to the centre of a wheel. Since, it is not easy to turn the rod without an aid; wheel is
used to rotate it. It acts as a speed-multiplier device.
Example: Door knobs, pedals of a bicycle, spindle tap, drilling machine.
4. What is a wedge? Explain the principal on which it works by giving suitable examples.
Ans: A wedge is a double inclined plane such that the two sloping surfaces taper to form either a sharp edge
or a pointed edge. When there are more than two sloping surfaces, they generally taper to form either a
very sharp or a pointed edge to split or pierce materials.
Example is the front end of a boat is shaped like a wedge so that it can easily cut across the flowing
water.
5. What is an inclined plane? What is the use of an inclined plane?
Ans: An inclined plane is a rigid sloping surface over which heavy loads can be raised or lowered to a
certain height or depth.
It is used to lift heavy loads with less effort.
• Numericals:
1. The length of a lever is 2 m. Calculate its mechanical advantage if the fulcrum is situated at a
distance of 40 cm from the effort.
Ans:
200 cm
E
40 cm
F
160 cm
L
Mechanical advantage = Effort arm ÷ Load arm = 40 ÷ 160 = 0.25.
2. The length of the load arm of a level is 6 m long & effort arm is 3 m long. What is the effort required
to lift a load of 40 N?
Ans: Load ÷ Effort = Effort arm ÷ Load arm
∴40 ÷ Effort = 3 ÷ 6
∴Effort = 40 × 6 ÷ 3 = 80 N.
3. Calculate the mechanical advantage of a crowbar of length 240 cm, if its fulcrum is situated at a
distance of 40 cm from the load.
Ans:
240cm
E
200 cm
F
40cm
L
Mechanical advantage = Effort arm ÷ Load arm = 200 ÷ 40 = 5.
4. What effort will be required to lift a load of 500 N by a single movable pulley?
Ans: Effort of 250 N is required because mechanical advantage of single movable pulley is 2.
Chapter-8 MAGNETISM
• Answer the following in short :
1. Give 2 examples each of magnetic & non-magnetic substances.
Ans: Magnetic substances: Iron, Nickel, and Cobalt.
Non-magnetic substances: Plastic, Wood, Wool, Paper & Rubber.
2. What is magnet? Differentiate between natural & artificial magnets.
Ans: A magnet is a piece of metal that can attract metals such as iron, nickel & cobalt.
Natural magnets
Artificial magnets
1. They are naturally occurring magnets.
They are made by people.
2. Ex: Loadstone or magnetite.
Ex: Bar magnets, horseshoe magnets, ring
magnets.
3. If a bar magnet is placed over iron filings, where will the attraction of the iron filings be
a) Maximum? b) Minimum?
Ans: The attraction of the iron filings will be maximum at poles and minimum towards centre.
4. Define the following:
1. Magnetic Axis: An imaginary line passing through the magnetic north pole & magnetic south pole of a
bar magnet is called its magnetic axis.
2. Effective length: The distance between the north pole & south pole of a magnet is called effective
length of the magnet.
3. Magnetic equator: An imaginary line bisecting the effective length of a magnet is called the magnetic
equator.
4. Magnetic field: The region around a magnet where its magnetic force can be experienced is called the
magnetic field.
5. Name a few common appliances that use electromagnets.
Ans: Common appliances that use electromagnets are electric bells, electric motors, loudspeakers,
telephones & generator.
6. How will you test if a given substances is a magnet or not?
Ans: Take a bar magnet & an unidentified metallic bar. Metallic bar is kept on a wooden table & a bar magnet
is brought close to one of its pole the following conditions can occur:
Bar is attracted
Bar is repelled
Bar is not attracted
Either (i) It is made of a magnetic
∴ It is magnet.
∴ Not a magnet
material or (ii) It is a magnet that
as it is made up
has its opposite pole facing the
of a non- magnetic
magnet. ∴It requires further
material.
investigation.
If bar is attracted so requires further investigation. Now, bring other pole of the magnet near the same end of
the metallic bar and the following conditions can occur:
Bar is attracted
∴Bar does not have
magnetic poles.
Bar is repelled
∴It is a magnet because this end
of the bar has same pole as the
end of the magnet facing it.
Thus, repulsion is the sourest test for magnetism.
5. Answer in detail:
1. Distinguish between a temporary magnet & a permanent magnet.
Temporary magnet
Permanent magnet
1.
It retains magnetic property for a short
It retains magnetic property even after the
duration of time.
magnetizing force is removed.
2.
It behaves like a magnet under the
It behaves like a magnet even in the absence
influence of an external magnetizing force.
of magnetizing force.
3.
Ex: Soft iron is used to make it.
Ex: Iron, steel, cobalt, nickel or an alloy called
ALNICO is used to make it.
2. Write a short note on the theory of magnetism.
Ans: In a magnetic substance, each individual particle behaves like an independent magnet. In the
unmagnetized state, these particles are present in a random fashion & hence they cancel out the
magnetic effects of each other. To magnetize a magnetic material, these tiny particles must be aligned in
a particles direction. The magnet will become stronger, if the alignment of particles is maximum. Refer
figure from text-book.
3. List methods of magnetizing a magnetic substance.
Ans: Methods of magnetizing a magnetic substance are single touch method, double touch method, by
induction and by electricity.
4. How can a magnet be demagnetized?
Ans: A magnet can be demagnetized by rough handling, hamming the magnet several times, dropping the
magnet on the floor several times, heating at a very high temperature, passing an AC current around the
magnet.
5. How can you make an electromagnet? State the characteristics of an electromagnet.
Ans: Coil the insulated copper wire around the ion. Connect the ends of the wire to the battery through the
switch. Close the switch so that current starts flowing. Now, bring ion paper pins close to the iron & paper
pins are attracted, showing that the iron has turned into an electromagnet.
Characteristics: (1) The strength can be increased by increasing the current in the coil. (2) They are very
strong temporary magnets. (3) As soon as the current is switched off, it becomes demagnetized. (4) Polarity
can be changed by changing the direction of current. (5) Made in different shapes & sizes according to the
requirements. (6) The strength can be increased by increasing the number of turns of the coil.
6. How is the single - touch method of magnetism different from the double - touch method?
1.
Single - touch method
One bar magnet is required.
Double - touch method
Two bar magnets are required.
2.
One pole of the magnet is placed over the
needle & slide it slowly along the needle to
the other end and needle behaves like a
magnet.
Opposite poles of the two bar magnets are
placed next to each other & are kept at the
centre of the needle & magnets slide along the
needle in opposite direction & needle behaves
like a magnet.