Download 10th Class Physics Notes (Unit # 10) for Federal Board (FBISE) Islamabad

Download 10th Class Physics Notes (Unit # 10) for Federal Board (FBISE) Islamabad.

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Download 10th Class Physics Notes for Federal Board (FBISE) Islamabad

What is simple harmonic motion? What are the necessary conditions for a body to execute simple harmonic motion?
The special kind of vibratory motion of a body, whose acceleration is directly proportional to its displacement from mean or equilibrium position, is called simple harmonic motion.
i)             Acceleration is directly proportional to its displacement.
ii)           Acceleration is directed towards the mean position.

Think of several examples in everyday life of motion that are simple harmonic.
i)             Oscillating simple pendulum
ii)           Oscillating mass spring system
iii)          Pendulum of wall clock

What are damped oscillations? How damping progressively reduces the amplitude oscillations?
The continuous decrease of amplitude of oscillator is called damped oscillator and the oscillations are called damped oscillations.
Simple harmonic oscillations are ideal. In case of real oscillator, there is continuous decrease of amplitude which ultimately becomes zero. It is due to resistance of medium which reduces the mechanical energy of system. This resistive force is called damping force.

How can you define the term wave? Elaborate the difference between mechanical and electromagnetic waves? Give examples of each.
Wave is the mean to transport energy from one place to another without transport of matter.
Mechanical Waves:
The waves which require medium for their propagation. For example sound waves, water waves and rope waves.
Electromagnetic Waves:
The waves which don't require any medium for their propagation. For example light waves are electromagnetic waves.
Distinguish between longitudinal and transverse waves with suitable examples.
The waves due to which the direction of oscillations are along the direction of propagation of waves are called "Longitudinal" waves. And the direction of oscillations are perpendicular to the direction propagation of waves are called transverse waves.
Examples of longitudinal waves:
i)      Sound Waves      ii)      Waves on slinky spring.
Examples of Transverse Waves:
i)      Water waves      ii)      String waves
Draw a transverse wave with amplitude of 2 cm and a wavelength of 4 cm. Label a crest and trough on the wave.
Derive a relationship between speed, frequency and wavelength of wave. Write a formula relating speed of a wave to its time period and wavelength.
If the speed of waves is (v) and the time period of the plate producing waves is T seconds, then the distance covered by the wave will be vT. As it is equal to the wavelength, therefore,
λ       =      vT
v      =      λ/T    or λ x 1/T
We know that 1/T=f then
V      =      f λ
Waves are the means of energy transfer without transfer of matter. Justify this statement with the help of a simple experiment.
If we hold an end of a long string and give it vibrations. Then a wave is set up on the string and the other end also starts vibrating automatically (after some time). It confirms the transfer of energy by the help of wave on string. It confirms the transfer of energy and not the transfer of mass.

Explain the following properties of waves with reference to ripple tank experiment.
When a waves strike an obstacle placed in its path, it will be reflected back in a particular direction. This phenomenon is called reflection of waves.
Laws of reflection are:
i)      Angle of incident ray (Angle i) and reflected ray (Angle r) will be equal.
ii)      (Angle i), (Angle r) and the normal, all lies at the same plane
When waves enter from one medium to another, a part of it is reflected in the same medium while the other part is transmitted into the other medium. This phenomenon is called refraction of waves.
The wave speed and wavelength of a wave change in the second medium but frequency does not change.
(*** draw figure from book)
The bending of waves around obstacles is called diffraction.
For example, radio and TV waves reach in those areas where they could not reach directly due to diffraction
Does increasing the frequency of a wave also increase its wavelength? If not, how are these quantities related?
We know the relation V        =f λ
It clearly shows if frequency increases then wavelength decreases because the product is constant that is velocity. Velocity is constant until medium is constant.

A ball is dropped from a certain height onto the floor and keeps bouncing. Is the motion of the ball simple harmonic? Explain.
As the ball is dropped from certain height “h” onto the floor having initial P.E = mgh and keeps bouncing. It is observed after each bounce its height and its P.E are decreasing. And time period is also decreasing. As time period is not constant and total energy is not conserved so the motion of the ball is not simple harmonic motion.

A student performed two experiments with a simple pendulum. He use two bobs of different masses by keeping other parameters constant. To his astonishment the time period of the pendulum did not change! Why?
Formula of time period of simple pendulum is independent of mass of bob. By change of mass of bob no change in time period is expected.

What types of waves do not require any material medium for their propagation?
Electromagnetic waves do not require any material medium for their propagation. For example X-ray, Radio waves, TV waves etc.

Plane waves in the ripple tank undergo refraction when they move from deep to shallow water. What change occurs in the speed of the waves?
When water waves coming from deeper portion of ripple tank enter into another region of shallow water region, then these show refraction. Their speed in both the regions is not same due to change of value of wavelengths.

Define vibrational motion.
The to and fro motion of a body about is its mean position is called vibrational motion. For example simple pendulum, flapping of wings of birds etc. The motion of vibrating body from one extreme position to other and then back to the same is called one vibration.

How spider detects its prey.
A spider detects its prey due to vibration produced in the web.

Define Time Period and Frequency?
  • The time to complete one vibration is called time period.
  • The number of vibrations in one second is called frequency.

What do you know about damping of shock absorber of automobiles.
Shock absorbers in automobiles are one of the practical applications of damping motion. A shock absorber consists of a piston moving through a liquid such as oil. When the car travels over a bump on road, the car may vibrate violently. The shock absorbers damp these vibrations and convert their energy into heat energy of the oil. Thus the passengers do not feel vibrations.

How pendulum clock was invented?
Christian Huygens invented the pendulum clock in 1656. He was inspired by the work of Galileo who had discovered that all pendulums of the same length took the same amount of time to complete one full swing.

What do you know about the speeds of Longitudinal and Transverse waves through various matters?
  • Longitudinal waves move faster through solids than through gases or liquids.
  • Transverse waves move through solids at a speed of less than half of the speed of longitudinal waves. It is because the restoring force exerted during this up and down motion of particles of the medium is less than the restoring force exerted by a back and forth motion of particles of the medium in case of longitudinal waves.

Which type of wave carry more energy. High frequency waves or low frequency?
To generate a high frequency wave required more energy per second, therefore high frequency waves carry more energy than low frequency waves.


Explain the motion of mass attached with a spring on a horizontal and frictionless plane is simple harmonic motion.
·         Consider the following figure.
(Draw figure from book)
·         In the figure, a spring is placed on a smooth surface. Its one end is attached to firm support. A mass ‘m’ is attached on its other end.
·         In this state, there is no extension in spring, i.e it is in equilibrium state.
·         If a force ‘Fext is exerted on mass toward right, the length of spring will be increased by an amount ‘x’. Mass will move from its position ‘O’ to ‘A’.
·         As per Hooke’s law
Fext    α      x
Fext    =      kx
·         Here k is a constant, and is called spring constant. Value of k is obtained by the equation (k = Fext/x)
·         The ratio of External Force (Fext) and increase in length (x) is called spring constant. Its unit is Nm-1.
·         After removing the External Force (Fext), spring moves towards its original position ‘O’. but now F = -kx
·         Acceleration ‘a’ of the mass ‘m’ can be found as (a = F/m = -kx/m). Acceleration is always directed towards its original position.
·         Due to inertia, mass ‘m’ does not stop  at ‘O’, but it reaches upto A’.
·         After reaching to A’, spring again tries to reach to its original position ‘O’, but again pass it.
·         In this way mass start moving to and fro about its original position ‘O’.
·         Therefore, motion of mass attached to spring is called simple harmonic motion.
·         Time Period (T) of mass attached to spring can be found by the following equation.

T      =      2 ∏   m/k

Definition of SHM:
“The acceleration of a body executing S.H.M is directly proportional to the displacement of the body from equilibrium position, and is always directed towards the equilibrium position.”

Kinetic and potential energies of mass attached to spring at different displacement.
  • Consider a horizontal spring-mass system. The mass is oscillating simple harmonic motion under restoring force.
  • At the mean position, it has maximum velocity so it has maximum kinetic energy and zero potential energy.
  • At the extreme position it has maximum potential energy and zero velocity so kinetic energy is zero.
  • At any displacement it has partially kinetic and partially potential energy, but total energy is constant.

Explain the motion of a ball in a bowl. Show that it is simple harmonic motion.
  • Consider a ball is placed at equilibrium position “O” the bottom of a bowl.
  • When the ball is at the bottom of the bowl, its weight mg is equal to the reaction R so net force is zero.
  • When a ball is gently displaced form the centre of a bowl it starts oscillating about the centre due to force of gravity which acts as a restoring force.
  • Once the ball is places at position A and then released, it will accelerate towards the mean position under its weight.
  • At the mean position it gains maximum velocity and momentum, so it moves up to the point B due to inertia.
  • At B it has zero velocity so zero kinetic energy but has maximum potential energy.
  • Again from point B it will move toward O under the restoring force having maximum velocity at O, but does not stop at O and will go up to A.
  • In this way the ball will continue to oscillate between the points A and B about point O, it has simple harmonic motion.

What is a simple pendulum; explain the motion of the bob is simple harmonic motion.
*See figure from book
·         Simple pendulum consists of a single isolated bob, which is suspended from a frictionless support by means of light inextensible string.
·         In equilibrium position, it is held stationary in vertical position and its bob is at ‘O’.
·         If the bob is disturbed from O to A, it start moving about its mean position. This to and fro motion is between points A and B.
·         Its acceleration remains towards ‘O’.
·         Hence, we can say that motion of simple pendulum is also simple harmonic motion.
·         Time period (T) of simple pendulum can be found by the following equation.

T      =      2 ∏   l/g
·         Where ‘l’ is the length of pendulum and ‘g’ is gravitational acceleration.

Write down the characteristics of SHM and give some examples from daily life?
i)             SHM is a vibratory motion.
ii)           A body doing S.H.M, always vibrate about its mean (equilibrium) position.
iii)          Its acceleration is always directed toward its mean position.
iv)         Its acceleration is directly proportional to its displacement from the mean position.
v)           Its velocity is maximum at mean position, and minimum at extreme positions.
vi)         The P.E is maximum at extreme position and zero at mean position.
vii)        Amplitude of oscillation for SHM remains constant.

Daily Life Examples:
·         An oscillating simple pendulum.
·         An oscillating mass spring system.
·         The motion of a ball and bowl system.
·         The motion of the prong of a tuning fork.

Explain the term wave. What are types of waves?
The periodic disturbance spreading all around inside a medium is said to form a wave. It has two types:
1-Mechanical Waves:
Waves that need a medium for their production and propagation are called mechanical waves. For example waves produced in water and string. Mehcanical waves have further two types:
  • Longitudinal Waves: Those waves in which the particles of the medium vibrate parallel to the direction of propagation of the wave are called compressional or longitudinal waves. For example sound waves.
  • Transverse Waves: Those waves in which the particles of the medium vibrate perpendicular to the direction of propagation of the wave are called transverse waves. For example waves produced by dipping a pencil in water. Those parts of transverse waves where the particles of the medium are above the normal position are called crest and parts where the particles of the medium are below their normal position are called trough.
2-Electromagnetic Waves:
The waves which do not require any medium for their propagation are called electromagnetic waves. For example X-ray, light waves, radio and TV waves.

Explain waves as carrier of energy and write the two methods of transfer of energy.
There are two methods of transferring energy.
i)             Through matter.
ii)           Through waves.
Through matter:
i)             When gun is fired, bullet get energy and moves towards target. When it hits the target, it transfers the energy to it. As a result breaking/damage takes place.
ii)           Running water in dams is also an example. Water transfers its K.E to turbine blades, due to which turbine start rotating and electricity is produced.
Through Waves:
i)             Fill a tub with water.
ii)           Move a rod up and down in it. Waves are produced in water and moves away from rod.
iii)          Place of cork on other end of tub on water surface.
iv)         You will see cork will also move up and down.
v)           In this process, energy supplied by rod and this energy transfers upto the cork by water waves.

Give the characteristics of wave motion.
Crests and Troughs:
The points at which the displacement is maximum are called crests and where the value of displacement of oscillations is minimum are troughs in a transverse waves.
The maximum value to displacement on either sides of mean position of an oscillatory proportion is called as amplitude.
The physical quantity which specify the value of displacement along with its direction w.r.t the mean position is called phase.
Wave length:
The distance between two successive points on a wave having same phases is called wave length.
One complete vibration is called one cycle.

The number of vibrations completed in one second is called frequency.
The time required to complete one vibration is called time period.
Wave front:
The imaginary surface touching all those points which are in same phase is called wave front.
Spherical Wave front:
The wave front due to waves generated by a point source, which spread all around the point source, from wave fronts in shape of concentric spheres.
Plane Wave front:
The wave front due to a number of waves moving parallel to one another is in shape of plane wave front.

What is ripple tank? Explain the construction and working of a ripple tank.
Simple apparatus, called ripple tank is used to observe the properties of waves (e.g. reflection, refraction, interference, diffraction etc).
Ripple Tank: -
·         This apparatus consists of a rectangular tray with glass bottom.
·         It is placed nearly half meter above the surface of a table.
·         Waves are produced on the surface of water with the help of a vibrator.
·         This vibrator is an oscillating electric motor which is fixed on a wooden plate.
·         This plate is suspended by means of rubber bands and its lower end touches the water surface.
·         On setting vibrator on, this plate starts vibrating and straight waves are generated on the water surface.
(***Draw Figure here from book.)
·         A bulb is hung over the tray. With the help of its light, the images of water waves is obtained on the white paper or screen.
·         The crests of the waves appear as bright lines on the paper because they function like convex lens and converge the rays of light falling on them.
·         The troughs of the waves appear as dark lines on the paper because they function like concave lens and diverge the rays.
·         To generate circular waves, the vibrating bar is raised up and a knob attached to it is lowered in such a way that it touches the water surface.
·         For the detailed analysis of these moving waves they should be frozen by one way or the other. This is done by means of a device called stroboscope.
·         Stroboscope consists of a round disc with slits on its edge.
·         This disk can be rotated about its centre by putting it into motion by a finger.
·         When we see through this disc, we see waves only, when a slit passes against our eye.
·         If we adjust the speed of stroboscope, so that a slit in front of our eye is replaced by another during the time in which the waves move forward by one wavelength, the waves appear to be stationary and we say that their motion is “frozen”.



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Download Class Notes: Download 10th Class Physics Notes (Unit # 10) for Federal Board (FBISE) Islamabad
Download 10th Class Physics Notes (Unit # 10) for Federal Board (FBISE) Islamabad
Download 10th Class Physics Notes (Unit # 10) for Federal Board (FBISE) Islamabad
Download Class Notes
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