TyroCity: Physics Notes

Gravitation

TyroCity.com — Sat, 12 Jul 2014 05:41:42 +0000

Gravitation
Every object in our universe attracts the other object with certain force towards its center. This force of attraction is known as GRAVITATIONAL FORCE and the phenomenon is called GRAVITATION. This is gravitational force which is responsible for the uniformity or regularity in our daily astronomical life. The whole system of the universe is in order only due to this force. Due to gravitation, the system of our universe is working uniformly and smoothly. The planets around the earth or around the sun moves in an orderly motion due to gravitation.

Newton's Law of Gravitation

In order to explain the gravitational force between two bodies, Newton formulated a fundamental law known after his name i.e. “NEWTON’S LAW OF GRAVITATION”

Newton’s law of gravitation states thatevery object in the universe attracts the other object with a force and :

(1) The gravitational force of attraction between two bodies is directly proportional to the product of their masses.

F a m1 x m2 ——- (1)

(2) The gravitational force of attraction between two bodies is inversely proportional to the square of the distance between their centers.

F a 1/r² ——— (2)

Mathematical Representation

Let us consider two bodies of masses m1 and m2 placed with their centres at distance of r from each other.

According to the Newton’s law of gravitation, the gravitational force of attraction between them is

F a m1 x m2 ——- (1)
F a 1/r¹ ——— (2)
F a m1m2 /r¹

Combining (1) and (2)

F = G m1m2/r¹

Where is the constant of proportionality.

G = universal gravitational constant

Value of G:

G = 6.67 x 10^-11 Nm²/kg²

Vectoral form of the law

The law of universal gravitation can also be expressed in vector form, which gives the magnitude as well as the direction of gravitational force.

The force exerted on body (1) by body (2) is always directed towards body (2) and acts along the line joining their centres
The displacement vector "r" from (2) to (1) is directed from body (2) to body (1), then,

The force exerted on body (2) by body (1) is always directed towards body (1) and acts along the line joining their centres
The displacement vector "r" from (1) to (2) is directed from body (1) to body (2), then,

The negative sign shows that the force of gravitation between two bodies is always an attractive force not a repulsive force.

Wave Motion

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Wave motion

Short Questions

How are stationary waves formed?
If you are moving on the moon surface, can you hear the cracking sound behind you? Explain.
Do sound waves undergo reflection, refraction and polarization phenomena? Explain.
Which type of wave propagates in liquid, explain.
Longitudinal waves cannot be polarized. Why?
Distinguish between light waves and sound waves.

Long Questions

Use the principle of superposition of two waves to find the position of displacement of nodes and antinodes in standing waves?
State and explain the stationary waves?
Define progressive wave. Derive progressive wave equation.
What do you mean by progressive wave equation? Derive progressive wave equation in terms of its wave vector and displacement.
What the principle of superposition is as applied to wave motion? Discuss, the result of superposing two waves of equal amplitude and same frequency travelling in opposite direction.

Diffraction

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Diffraction grating is better than a two –slit set up for measuring the wave length of monochromic light. Explain.
What is diffraction of light?
Radio waves diffract around building but light waves do not. Why?
The diffraction of sound waves is more evident in daily experience than that of light waves, why?
Describe what happens to the single slit diffraction pattern when the width of the slit is less than the wave length of the wave.
What is self-inductance? Define coefficient of self-inductance.
What is diffraction of light? How does it differ from interference of light?
Describe the diffraction of light at a single slit and find the condition for secondary maxima and minima.
What are the difference between interference and diffraction? Explain the theory of diffraction off light through a single slit.
Describe diffraction of light through a single slit.
What is the basic difference between interference and diffraction? Discuss Fraunhofer diffraction at a single slit.
What is Fraunhoffer diffraction? Explain the formation of maxima and minima due to diffraction? Show that the width of central maxima is inversely proportional to the distance between the two slits.

DC Circuit

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Short Questions

An ammeter is always connected in series. Why?
Why do we use connecting wires made of copper?
What are the factors on which the resistance of a conductor depends?
Can the potential difference across a battery be greater than its emf?
Two bulbs of 60 W and 100 W are connected in series and this combination is connected across the mains. Which bulb will glow more brightly? Give reason.
You are given n wires each of resistance rΩ. What is the ratio of maximum to minimum resistance that can be obtained from these wires?
Is terminal p.d. always connected in parallel with the load resistance?
Two bulbs have the filament of the same length. If one is of 40 watt and the other 60 watt, which one has thicker filament?
Two bulbs have the filament of the same length. If one is of 40 watt and the other 60 watt, which one has thicker filament?
Why are alloys constantan and manganin used to make standard resistors?
A large number of free electrons are present in metals. Why is there no current in the absence of electric field across it?
Explain the significance of a shut with a diagram.
The element of heater is very hot while the wire carrying current are cold, why?
You are given 2 wires each of resistance R. What is the ratio of maximum to minimum resistance that can be obtained from these wires?
Why heat is generated across a resistor when the electric field is applied?
Why do electric acquire a steady drift velocity?
Why ammeter is always connected in series?
A wire is stretched to double its length. What happens to its resistance?
The energy that can be extracted from a storage battery is always less than the energy that goes into it while charging. Why?
The resistance of an ammeter must essentially be very small. Why?
Water boils in an electric kettle in 15 after being switched on. Using the same main supply. Should the length of the heating element be increased or decreased if the water is to boil in 10 minutes? Explain.
What is the ratio of maximum to minimum resistance obtained from n wires of resistance R each?
Why is it essential that the resistance of a voltmeter be very high?
An ammeter is always connected in series. Why?
Distinguish between resistance and resistivity of a material.
Long-distance, electric power, transmission lines always operate at very high voltage, some time as much as 750 kV. What are the advantages of such high voltage?
Distinguish between resistance and resistivity. Derive expressions for the effective resistance of number of resistors connected in series and parallel.

Long Questions

Deduce an expression for the heat developed in a wire by the passage of an electric current.
What do you mean by a shunt? Describe its use in converting a galvanometer into an ammeter.
What is drift velocity of an electron? Derive a relation between the current through a metallic conductor and the drift velocity in terms of the number of free electrons per unit volume of the conductor.
Discuss the mechanism of metallic conduction. Derive j=new where j is the current density, e is the electronic charge and v is drift velocity.
State and explain joule`s laws of electric current. Discuss how they are verified experimentally.
What do you meant by shunt? How will you convert a galvanometer into an ammeter?
State and explain Ohm`s law. Two resistors are connected in parallel and third resistor be connected in series with the combination of parallel resistors. If this combination be connected with a battery of the negligible internal resistance, find the potential difference across each resistor.
What is meant by a shunt? How will you convert a galvanometer into a ammeter?
Discuss the mechanism of metallic conduction. Derive a relation between current density and drift velocity.

Electrical Circuits

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Short Questions

State Kirchhoff`s laws of circuits.
Why does voltmeter measures current more accurately than an ammeter?
What is Wheatstone bridge? Obtain the balanced condition for the bridge? Explain how resistance can be measured by a meter bridge?

Long Questions

What is a Wheatstone bridge? Using Kirchhoff`s law, derive the principle of Wheatstone bridge.
What is a potentiometer? Explain how you compare the emfs of two cells using a potentiometer.
Discuss the principle of potentiometer and use it to determine the internal resistance of a cell.
Discuss the principle of the potentiometer and use it to compare the emfs of two cells.
Explain the principle of the potentiometer. How is this used to measure the internal resistance of a cell?
State and explain Joule`s law of heating. Deduce an expression for the heat developed in a wire by the passage of an electric current?
What is potentiometer? How can you use it to measure internal resistance of a cell?
What is internal resistance of a cell? How can you measure the internal resistance of a cell by using potentiometer?
What is the principle of potentiometer? Describe a method to measure the internal resistance of a cell by using potentiometer.
What is Wheatstone bridge? Derive the principle of Wheatstone bridge using Kirchhoff`s Law.

Mechanical Waves

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Short

Why sound made/produced at a distance can be heard distinctly at night than in the day time?
Is velocity of sound more in damp air or in dry day?

3.Why sounds are heard better on a wet day than on a dry day?

Do sound waves need a medium to travel from one point to other point in space? What properties of the medium are relevant?
Although the density of solid is high, the velocity of sound is great in solid, explain.
Explain why the velocity of sound in solids is greater than that in gases, though the densities of solids are greater than that of gases.
Sound at distances can be heard distinctly at night than in the day time. Why?
Velocity of sound increases on a cloudy day. Why?
Sound travels faster in metal than in air, why?
Can two persons on hear the sound of each other? Explain.

Long

Discuss the effect of pressure, temperature and density of elastic medium on the velocity of sound.
What is Newton`s formula for the velocity of sound? What correction was made by Laplace?
Describe Newton`s expression for the velocity of sound in a gas.
Derive an expression for the velocity of sound in a medium by dimensional method. Discuss the effect of change in pressure and temperature on the velocity of sound in air.
Discuss Laplace`s correction and derive the formula for the velocity of sound in a gas.
State Newton`s formula for the velocity sound in gases. What correction was done by Laplace on it?
Explain the significance of Laplaces correction of Newtons formula for the velocity of sound derive the corrected formula.
Write down the factors on which the velocity of sound in air depends with necessary explanation.
Discuss Newtons formula for the velocity of sound in a gas with Laplaces correction.
Discuss Newtons formula for the velocity of sound in air with Laplaces correction.
Write an expression for the speed of sound in an ideal gas. Discuss the effect of change in temperature on the speed of sound.

Magnetic effect of current

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Short Questions

Under what conditions do a charge affect a magnet?
State Ampere’s theorem
Does a charged particle moving through a magnetic field experience a force? Express with conditions, maximum, and minimum force it experiences.
A portion moving in a straight line enters a strong magnetic field along the field direction. How will its path and velocity change?
Why is the cylindrical core of soft iron used in moving coil galvanometer?
Define an Ampere in terms of the force between current carrying conductors.
How magnetic field is made radial in a moving coil galvanometer?
Explain how the direction of Lorentz force is determined.
A current carrying solenoid tends to contract, why?
A solenoid tends to contract when a current passes through it, why?
What will be the effect if the magnetic field in a moving coil galvanometer is not radial?
An electron beam and a portion beam are moving parallel to each other is the beginning. Do they always maintain this status? Justify your answer.
Deduce an expression for the force between two parallel current carrying conductors. Define one ampere current.
State Ampere`s circuital theorem.

Long Questions

State Biot-Savart law and obtain the expression for the magnetic field at the centre of the circular coil.
Explain in brief, the motion of an electron moving normal to a magnetic field.
Derive an expression for the magnitude of the magnetic flux density at the centre of a narrow circular coil.
Derive an expression for the magnetic field at a point due to a long straight conductor carrying current.
What is a Helmholtz coil? Derive an expression for the magnetic field due to this coil.
Derive the formula for the magnetic field at the centre of the circle of a circular coil carrying current. Explain why the magnetic field at the centre of the coil disappears when the circular coil is made infinitely large.
State and explain Ampere`s theorem and hence use it to find the magnetic field intensity due to a long current carrying solenoid.
Derive the formula for the magnetic field at a point due to a long straight current carrying conductor using Biot- Savart law.
State and explain Biot-Savart law and hence use it to find the magnetic field intensity at any point due to a long straight conductor.
Find an ex expression for torque on rectangular coil in a uniform magnetic field.
What is a Helmholtz coil? Derive an expression for the magnetic field due to this coil.
State and explain Biot-Savart law. Use this law to find the magnetic field intensity at any point due to a long straight current carrying conductor.
State and explain Boit-Savart law with a case of its application.
Derive an expression of force per unit length between two parallel conductors separated by distance ‘r’ and carrying currents l1 and l2 in the same direction.
State and explain Biot-Savart law. Use it to find the magnetic field at the center of a circular coil of N turns and carrying current l.
Find an expression for the magnetic field on the axis of a solenoid, carrying current, using Ampere`s law.
Obtain magnetic field straight at a point on the axis of circular current loop by using Biot and Savart law.
State and explain Ampere`s theorem and hence use it to find the magnetic field due to a long solenoid carrying current l.
Straight and explain Biot-Savart law and hence use this law to find the magnetic field to a long straight current carrying conductor.
What is a Helmholtz coil? Derive an expression for the uniform magnetic field obtained from it.

Alternating Currents

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Short Questions

Why do we prefer a choke coil to rheostat in an a.c. current?
What is meant buy independence of an a.c. current?
Why is choke coil preferable to resistor?
Why is choke considered superior to a rheostat?
What do you mean by r.m.s value of an AC current?
What is meant by wattles current?
Fluorescent tubes often use an inductor to limit the current through the tube. Why is it better to use inductor than a resistor for this purpose?
Why is a choke coil better than a resistor ina n electrical appliences?
Define rms value of alternating current.
What are the advantages of a.c. over d.c.?
A chock coil is preferred to a resistor in an ac current. Why?

Long Questions

Discuss the phase relationship between the voltage and current in the ac current containing inductance and resistance. What is power factor of the circuit?
Find the impendence of LCR circuit in series.
An alternating emf is applied across a capacitor. Show that the current in its leads to the applied emf by 90°.
An a.c. passes through a circuit containing a resistor and a inductor in series. Derive an expression for the phase relation between the current and the voltage.
Discuss the phase relationship between the voltage and current in the a.c. circuit containing capacitor and resistor in series and hence derive an expression for the impedance of the circuit.
Derive the condition for resonant frequency of an LCR alternating current series circuit.
Derive an expression of current flowing through a.c. circuit containing a resistor and capacitor in series combination. What is the power factor of this circuit?
Discuss the phase relationship between the circuit and voltage in a.c. circuit containing capacitor and resistor in series and hence derive an expression for the impedance of the circuit.

Acoustic Phenomena

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Short Answer Questions

How are beats produced? What is beat frequency?
What are ultrasonic and infrasonic?
Distinguish between ultrasonic and supersonic’s.
How it is that one can recognize a friend from his voice without seeing him?
Why is it roaring of a lion different than the sound of a mosquito?
What do you mean by the term threshold of hearing?
Whistle of an approaching train is shriller. Why?
Define beats and beat frequency.
Bells are made of metal and not of wood, why?
Explain with a figure the meaning of beats.
Two notes, one produced by violin and the other by a sitar, may have the frequency, yet we can distinguish between them. Why?
Which has a more direct influence on the sound wave: the observer is approaching the stationary sound source.
What is meant by threshold of hearing?

Long

Deduce the expressions for the frequency herd by an observer, when the observer is approaching the stationary sound source.
What is Doppler`s effect? Derive an expression for the apparent frequency received by a stationary observer when a source is moving away from him.
What do you mean by intensity and intensity level of sound? Define bel and decibel.
What are beats? Prove that the number of beats per second is equal to the difference between the frequencies of two superposing waves.
What is Doppler`s effect? Derive the change in frequency when an observer moves towards a stationary source?
Discuss the phenomenon of Doppler`s effect. Find the change in frequency when a moving source of sound passes a stationery observer.
Define intensity of sound. Show that the intensity of sound for a given frequency is directly proportional to the square of amplitude of vibration.

8 Define the intensity of sound and prove that l=1/2pVr2w2 where the symbols have their usual meaning.

What is the Doppler Effect in sound? Obtain an expression for the apparent frequency of the sound when the source and observer both move in the same direction.
Define intensity and deduce it in terms of amplitude of vibration, density of medium, angular velocity and velocity of the wave.
What are beats? Obtain an expression for the beat frequency when beats are produced by superposing two waves of slightly different frequencies.
What is Doppler`s Effect? Deduce an expression for the apparent frequency heard by a stationary observer when a source approaches towards him.

Electromagnetic Induction

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Short Questions

What is Lenz’s law?
Mention two types of loss in a transformer.
Show that Lenz’s law is an example of conservation of energy.
Two closely would circular coils have the same number of turns, but one has twice the radius of the other. What is the ratio of self inductance’s of the two coils?
Why can`t a transformer be used to change the value of d.c. voltage?
What is eddy current? Write down its uses?
What are different power losses in a transformer? What measures do you take to minimize these losses?
Why can`t a transformer be used to step up or down the d.c. voltage?
A transformer cannot be used in do circuits, why?
State Faraday`s laws of electromagnetic induction.
A sheet of copper is placed between the poles of an electromagnet with the magnetic field perpendicular to the sheet. When it is pulled out, a considerable force is required, and the force required increases with speed, why?
Permanent magnets are made of steel while the core of transformer is made of soft iron. Why?
A student asserted that if a permanent magnet is dropped down a vertical copper pipe, it eventually reaches a terminal velocity even if there is no air resistance. Why should this be?
If a permanent magnet is dropped down a vertical copper pipe, it eventually reaches a terminal velocity even if there is no air resistance. Why should this be?
Describe the theory and working of an a.c. generator.

Long Questions

Obtain the expression for the emf induced in the conductor moving in a magnetic field.
State the laws of electromagnetic induction. Derive an expression for the emf induced in a conductor moving in a magnetic field.
Deduce an expression for induced emf in a coil rotating in a magnetic field.
State Lenz`s law and explain how this law leads to the conservation of energy principle.
State Faraday`s laws of electromagnetic induction. Deduce an expression for induced emf in a coil rotating in a magnetic field.
State and explain Faraday`s law of electromagnetic induction. Derive an expression for the induction a coil rotating in a uniform magnetic field.
State Faraday`s law of electromagnetic induction. Derive an expression for the induced in a straight conductor moving at right angle to the direction of a uniform magnetic field.
A metallic rod is moving in a magnetic field. Determine the emf induced across it.

Polarization

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Short answers question

Can sounds waves be polarized? Explain.
Is polarization possible for longitudinal waves? Why?
Light waves can be polarized. What about sound waves? Explain.
What is polarizing angle? Does it depend on the wavelength of light?
The polarizing angle for a transparent medium is 600. What is the refractive index of the medium?

Long answers question

Distinguish between a plane polarized and unpolarized light.
Show that: tan p=n
Where
n=refractive index of the medium
p=angle op polarization of polarizing angle.
What do you mean by polarization of electromagnetic waves? Discuss the polarization of light by refection and show that , where the symbols have their usual meanings.
What is polarizing angle? Derive the relation between the polarizing angle and the refractive index of the medium.

Physics XII Questions

Physics XII Notes — Sat, 12 Jul 2014 05:41:42 +0000

Unit 1: Waves and Optics

Waves

Physical Optics

Unit 2: Electricity and magnetism

Current Electricity

Magnetic Field of current

Other topics

Free question test - Physics 12