TyroCity: Physics Notes

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.

Mechanical Waves: Important Questions

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

What do you mean by water waves?
Why sound produced at a distance can be heard distinctly at night than in day time?
Is velocity of sound more in damp air or in dry air? Explain.
A boat at anchor is rocked by waves whose crest is 100 feet apart and whose velocity is 25 feet /s. These reach the boats once in every t s. What is the value of t?
Ultrasonic, infrasonic and audio waves travel through a medium with velocity vu, vi, varespectively. Then what is the relationship among them?
A man stands on the ground at a fixed distance from a siren whit emits a sound of fixed amplitude.
The ratio of velocity of sound in hydrogen gas r=7/5 to that on helium gas r= 5/3 at the same temperature is VH:VHe, what is the value of this ratio?
The velocity of sound in a tube containing air at 27°C at the pressure of 760 cm of Hg is 330 m/s. What will be the velocity of sound when the pressure is increased to 100 cm of Hg and temperature is kept constant?
A uniform rod of length L and mass M hangs freely from a fined point. Then the velocity of transverse wave along the rod at a distance x from the free end is v m/s. What is its value?
In a ripple tank when one pulse is sent every 10th of a second, the distance between consecutive pulses is 30 mm. in the same depth of water pulse are produced in half second intervals. What is the distance between consecutive pulses?
If you are walking on the moon surface, can you hear the cracking sound behind you? Explain.
Do sound waves need a medium to travel from one point to other point in space? What properties of the medium are relevant?
Why velocity of sound in solid is more than that in liquid?
Why velocity of sound in liquid is more than that in air?
Why velocity of sound in hydrogen is more than that in air?
What are the draw backs of Newton’s formula for the velocity of sound in air? What is the Laplace’s correction?
What is the sound of clock tower heard feebly at large distance than near to it?
What is beat? How a musician can use this effect to tune string instrument?
What is threshold of hearing and threshold of pain?
Why are beats produced? What is beat frequency?
What is it that one can recognize a friend from his voice without seeing him?
Whistle of an approaching train is shriller. Why?
Although the density of solid is high, the velocity of sound is greater in solid, explain.
Why is roaring of the lion different than that of mosquito?
What is persistence of hearing? Also define threshold of hearing (or audibility) threshold.
Why is the wall at the back of the stage in a big hall made parabolic?
A stone is dropped from the top of the tower 300m high splashes into the water of a pond near the base, of the tower. When is the splash heard at the top? Given that the speed of sound in air is 340 m/s, g= 9.8 m/s [ ans= 8.70 s]
The audible frequency range of a human air is 20Hz to 20KHz. Convert this into the corresponding wavelength range. V of sound on air = 340 m/s.
Draw the graph for beat phenomenon.

Magnetic Properties of Materials

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

Short Questions

What are magnetic domains?
What is angle of dip? How does it vary from the equator to the poles/
Define angle of dip and angle of declination at a place.
How does dip vary from place to place on earth`s surface?
Why does a bar magnet not retain its magnetism when it is method?
Why does a magnet lose its magnetism when heated to high temperature?
Above Curie temperature a ferromagnetic material becomes paramagnetic. Why?
What are the characteristics of a Ferro-magnetic substance?
A permanent magnet can be used to pick up a string of nails, tacks or paper clips, even though these are not magnets by themselves. How can this be?
A ferromagnetic substance becomes paramagnetic above Curie temperature. Explain why?

Long Questions

The angle of dip in Britain is greater than that in Kathmandu. Why?

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

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.

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.

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.

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.

Free question test - Physics 12

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

Current Electricity

Discuss the mechanism of metallic conduction. Derive a relation between current density and drift velocity.
How is a galvanometer converted into an ammeter and to voltmeter? Explain?
Distinguish between resistance and resistivity. Derive expression for the effective resistance of number of resistors, connected in series and parallel.
Wave and Sound
What is resonance? How is the velocity of sound in air determined by resonance tube method?
What is the principle of super position as applied to wave motion? Discuss, the result of superposing two waves of equal amplitude and same frequency travelling in opposite direction.
What do you mean by phase oscillation and phase constant? Establish the equation of progressive wave.
Magnetic Effect if Current
Define radial magnetic field. Derive an expression for the torque on a rectangular coil in a uniform magnetic field and mention the condition for maximum and minimum torque.
Derive an expression for the magnetic field intensity at a point due to a current carrying straight conductor of infinity length, using Biot-Savart law.
Obtain an expression for the torque acting on a rectangular coil in a uniform magnetic field and also define magnetic moment.

Modern Physics

Describe J.J. Thomson’s experiment for determining the specific charge of an electron.
Describe the phenomenon of electrical discharge through gases.
Describe with necessary theory of Millikan’s oil drop experiment to determine the value of the charge particle in electric and magnetic field.
Discuss the productivity of cathode ray and its characteristics.

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.

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.

Chemical Effect Of Current

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

Short Questions

What is meant by Faraday’s Constant?
What is the function of copper sulphate used in Daniel cell?
Define one Faraday?
Distinguish between ionic and electronic conduction.

Long Questions

State and explain Faraday’s law of electrolysis. Hence, define Faraday’s Constant.
State the Faraday’s laws of electrolysis and verify the second laws.
State Faraday’s law of electrolysis. Discuss the experiment to verify them.