Distinguish Between

Distinguish Between

Chapter 1. Rotational dynamics

(2 marks each)

(1) Uniform circular motion and nonuniform circular motion.

Ans. Uniform circular motion (UCM)

1. A particle in UCM moves in a circle or circular are at constant linear speed and constant angular velocity.

2. The tangential and angular accelerations are zero.

3. The net linear acceleration is centripetal, i.e., radially inward.

4. The magnitudes of centripetal acceleration and the centripetal force are constant.

Nonuniform circular motion

1. For a particle in nonuniform circular motion in a plane, its linear speed and angular both change with time.

speed

2. The tangential and angular accelerations are non-zero.

3. The net linear acceleration, being the resultant of the radial and tangential accelerations, is not radial.

4. The magnitudes of the centripetal acceleration and the centripetal force are not constant.

(2) Centripetal force and centrifugal force.

Ans.

Centripetal force

1. Centripetal force is the force required to provide centripetal acceleration to a particle so that it moves in a circular path.

2. At every instant, it is directed radially towards the centre of the circular path.

3. It is a real force arising from gravitational or electromagnetic interaction between matter.

Centrifugal force

1. The centrifugal tendency of the particle, in its accelerated (non- inertial) frame of reference, is explained by assuming a centrifugal force acting on it.

2. At every instant, it is directed radially away from the centre of the circular path.

3. It is a pseudo force since it is the effect of the acceleration of the reference frame of the revolving particle.

Chapter 2. Mechanical properties of fluids

(3) Streamline flow and turbulent flow.

Ans. Streamline flow

1. The steady flow of a fluid, with velocity less than certain critical velocity, is called streamline or laminar flow.

2. In a streamline flow, the velocity of a fluid at a given point always constant. is

3. Streamlines do not change and never intersect.

4. The fluid flow is laminar over a surface, and is in the form of coaxial cylinders through a pipe.

Turbulent flow

1. It is a non-steady irregular fluid flow with a velocity greater than certain critical veloci certain critical

2. In a turbulent flow, the verouny of a fluid at any point does not remain constant.

3. Streamlines and flowtubes change continuously.

4. Fluid particles still move in general towards the main. direction as before. But now all sorts of secondary motions cause eddies or vortices.

Chapter 5. Oscillations

(4) Simple pendulum and a conical pendulum.

Ans. Simple pendulum

1. The oscillations of the bob are in a vertical plane.

2. The energy of the bob transfers back and forth between kinetic energy and potential energy, while its total mechanical energy remains constant.

3. The period depends on the length of the string and the acceleration due to gravity. T=2π/Lig

Conical pendulum

1. The bob performs UCM in a horizontal plane and the string traces out a cone of constant semivertical angle.

2. The gravitational PE of the bob being constant may be taken to be zero. The total mechanical energy remains constant and is entirely kinetic.

3. The period depends on the length of the string, the acceleration due to gravity and cosine of the semivertical angle.

Chapter 6. Superposition of waves

(5) Free vibrations and forced vibrations.

Ans. Free vibrations

1. Free vibrations are produced when a body is disturbed from its equilibrium position and released.

2. The frequency of free vibrations depends on the body and is called its natural frequency.

3. The energy of the body remains constant only in the absence of friction, air resistance, etc.

Forced vibrations

1. Forced vibrations are produced by an external periodic force of any frequency.

2. The frequency of vibrations is, in general, different from the natural frequency of the body.

3. The amplitude of vibrations is usually very small.

4. Vibrations stop in a short time 4 when the external force is removed.

(7) Progressive and stationary waves.

Ans. Progressive waves

1. Progressive waves are produced when a disturbance is created in the medium.

2. They continuously travel away from the source and transport energy through the medium.

3. Every particle vibrates with the same amplitude.

4. Phase changes from particle to particle.

5. Every particle of the medium is set into vibrations by these waves.

Resonance

1. Resonance is produced by an external periodic force whose frequency is equal to the natural frequency of the body, or nearly so.

2. For low damping, the frequency of vibrations is nearly the same as the natural frequency of the body.

3. The amplitude of vibrations is large.

. Vibrations continue for relatively long time even after the external force is removed.

Stationary waves

est

Ans.

1. Stationary waves are produced due to interference, under certain conditions, between two identical progressive waves travelling in opposite directions.

2. They do not move in any direction and hence do not transport energy through the medium.

3. Amplitude of vibration is different for different particles.

4. All the particles in the same loop have the same phase, while the particles in adjacent loops are in opposite phase.

5. There are some particles of the medium which do not vibrate at all.

(8) Harmonics and overtones.

Ans.

Harmonics

1. The lowest allowed natural frequency of vibration (fundamental) of a string (or air column) and all its integral multiples are called harmonics.

Overtones

1. The higher allowed frequencies of vibration above the fundamental are called overtones.

2. The lowest allowed natural frequency (fundamental), n, is called the first harmonic. The second harmonic is 2n, the third harmonic is 3n, ... and so on.

2. Above the fundamental, the first allowed frequency is called the first overtone which may be either the second or third harmonic. Depending on the system, the pth overtone corresponds to (p+1)th or (2p+1)th harmonic.

(9) Stationary waves and beats.

Ans. Stationary waves

1. Stationary waves are formed due to interference, under certain conditions, between two identical progressive waves travelling in opposite directions.

Beats

1. Beats are interference formed due to between two progressive waves which need not be travelling in opposite directions.

2. Interfering waves must have the 2 same frequency.

3. At a given point, the amplitude is constant.

4. Nodes and antinodes are produced.

5. The resultant wave does not travel in any direction.

6. There is no energy transport through the medium.

. Interfering waves must have slightly different frequencies.

3. At a given point, the amplitude changes with time.

4. There is waxing and waning of resultant intensity.

5. The resultant wave travels in the forward direction.

6. There is energy transport through the medium.

Chapter 7. Wave optics

(10) Interference and diffraction.

Ans. Interference

1. The term interference is used to characterise the superposition of a few coherent waves (say, two).

Diffraction

1. The term diffraction is used to characterise the superposition of a large number of waves coming from different parts of the same wavefront.

2. Double-slit interference fringes are all of equal width.

2. In single-slit diffraction pattern, only the non-central maxima are of equal width which is half of that of the central maximum.

3. In double-slit interference, bright fringes are of equal intensity.

3. In diffraction, successive non- central maxima decrease rapidly in intensity.

Chapter 8. Electrostatics

(11) Electric field intensity and electric potential.

Ans. Electric field intensity

1. Electric field intensity is a vector quantity associated with an electric field.

2. It is the electric force per unit positive charge placed at a point in an electric field. Its magnitude at a point is equal to the negative of the potential gradient at that point.

3. Its SI unit is the newton per coulomb or the volt per metre.

Electric potential 

1. Electric potential is a scalar quantity associated with an electric field.

2. It is the work per unit charge which must be done by an external agent against the electric force to bring an infinitesimal positive charge from infinity to a given point in an electric field, without acceleration.

3. Its SI unit is the volt.

(12) Volt and electronvolt.

Volt

1. The volt is the SI unit of electric potential (or potential difference).

Electronvolt

1. The electronvolt is a non-SI unit of energy.

2. It is the increase in the kinetic energy of a particle carrying a charge equal to the elementary charge e when it is accelerated through a potential difference of one volt.

2. If one joule per coulomb of work is done by an external agent against the electric force in moving an infinitesimal charge from one point to another keeping the charge in equilibrium, the potential difference between the two points is called one volt.

3. 1 V1 J/C.

(13) Series and parallel combinations of capacitors.

Ans.

Series combinations of capacitors

1. The capacitors are connected end to end and a cell is connected across the combination.

2. Equivalent capacitance is less than the smallest capacitance in series. For several capacitors of given capacitances, the equivalent capacitance of their series combination is minimum.

3. All capacitors in the combination have the same charge but their potential differences are in the inverse ratio of their capacitances.

3. 1 eV1.602 x 10-19 J.

Parallel combinations of capacitors

1. The capacitors are connected between two common points and a cell is connected across the combination.

2. For several capacitors of given capacitances, the equivalent capacitance of their parallel combination is maximum.

3. The same voltage is applied to all capacitors in the combination, but the charge stored in the combination is distributed in proportion to their capacitances.

Chapter 9. Current Electricity

(14) Potentiometer and voltmeter..

Potentiometer (March '22)Voltmeter

L. A voltmeter can be used to measure the potential difference and terminal voltage of a cell. But it cannot be used to measure the emf of a cell.

1. A potentiometer is used to determine the emf of a cell, potential difference and internal resistance.

2. Its accuracy and sensitivity are very high.

2. Its accuracy and sensitivity are less as compared to a potentiometer.

3. It is not a portable instrument.

3. It is a portable instrument.

4. It does not give a direct reading.

Chapter 11. Magnetic Materials

(15) A paramagnetic material and a ferromagnetic material.

Ans. Paramagnetic material

1. A material whose atoms possess a net magnetic moment that are all randomly oriented in the absence of an external magnetizing field is called a paramagnetic material.

2. It gets weakly magnetized when placed in an external magnetic field but its magnetization becomes zero when the external magnetic field is removed.

4. It gives a direct reading.

material whose ato atoms/ Digest

Ferromagnetic material

1. A molecules possess a net magnetic moment which interact strongly through exchange interaction forming domains, each of which spontaneously 272/44 saturation, is 4 to

ferromagnetic material.

2. It gets strongly magnetized even when placed in a weak magnetic field and retains some magnetization after the external magnetic field is removed.

3. Zm is small and positive, u, is slightly greater than 1.

3. %m and u, are positive and very high.

(16) A ferromagnetic material and a diamagnetic material.

Ans. Ferromagnetic material

1. A material whose atoms/ molecules possess permanent magnetic moment which interact strongly through exchange interaction to form magnetic domains, each of which is magnetized to saturation, is called a ferromagnetic material.

2. It gets strongly magnetized in the 2 direction of the field even when placed in a weak magnetic field and retains some magnetization after the external magnetic field is removed.

3. Zm and u, are positive and very high.

Diamagnetic material

1. A material whose atoms/ molecules do not possess a net magnetic moment in the absence of an external magnetic field is called a diamagnetic material.

2. The strength of an electromagnet depends on the magnitude of the current through the solenoid and the number of turns per unit length of the solenoid.

3. For a good electromagnet, the retentivity and coercivity of the core material should be low.

. In an external magnetic field, it gets weakly magnetized in the direction opposite to the field but its magnetization becomes zero when the external magnetic field is removed.

3. Zm is small and negative slightly less than 1.

(17) Electromagnet and permanent magnet.

Ans. Electromagnet

1. Magnetic field of an electromagnet is retained till there is passage of electric current through the solenoid or coil.

2. The strength of an electromagnet depends on the magnitude of the current through the solenoid and the number of turns per unit length of the solenoid.

3. For a good electromagnet, the retentivity and coercivity of the core material should be low.

Permanent magnet

1. Magnetic field is retained for a long period of time.

2. The strength of a magnet depends upon the nature of the material of which it is made.

3. For a good permanent magnet, the retentivity and coercivity of the material should be high.

Chapter 12. Electromagnetic Induction

(18) Step-up and step-down transformers.

Ans. Step-up transformer

1. The output voltage is more than the input voltage.

2. The number of turns of the secondary coil is more than that of the primary coil.

3. The output current is less than the input current.

4. The primary coil is made of 4 thicker copper wire than the secondary coil.

Step-down transformer

1. The output voltage is less than the input voltage.

2. The number of turns of the secondary coil is less than that of the primary coil.

3. The output current is more than the input current.

. The secondary coil is made of thicker copper wire than the primary coil. hool pol Digest

Chapter 13. AC circuits

(19) Resistance and reactance.

Ans. Resistance

1. Resistance is the property of a circuit element due to which electrical power is dissipated in the element by Joule heating.

2. Resistance of a circuit element is independent of the frequency of the applied alternating emf unless the frequency is very high.

Reactance

1. Electrical power is not dissipated in a circuit element by Joule Cheating due its reactance.

The energy is stor electric field of the magnetic f4 inductor-and transferred back to the supply.

2. Reactance of a circuit element depends on the frequency of the applied alternating emf.

Chapter 15. Structure of atoms and nuclei

(20) Nuclear fission and nuclear fusion.

Ans. Nuclear fission

1. It is a nuclear reaction in which a heavy nucleus of an atom, such as that of uranium, splits into two or more fragments of comparable size.

2. Nuclear fission occurs either spontaneously or as a result of bombardment of a neutron on the nucleus (induced fission).

3. Controlled induced fission chain reaction is used in a nuclear reactor to generate electricity.

Nuclear fusion

1. In nuclear fusion, lighter atomic nuclei (of low atomic number) fuse to form a heavier nucleus (of higher atomic number).

2. Very high temperatures above of 10K, are required to carry out nuclear fusion.

3. Nuclear fusion reactions in the interior of stars are the source of their energy output and the means of synthesis of higher elements like carbon, nitrogen and silicon from hydrogen and helium. D

Chapter 16. Semiconductor devices

(21) Light emitting diode and photodiode.

Ans. Light emitting diode

1. It is a forward biased pn-junction diode formed from a compound semiconductor.

3. The intensity of the emitted light is directly proportional to the diode forward current.

Photodiode 4

1. It is a special purpose reverse

biased pn-junction diode.

2. It emits light due to direct 2. It generates charge carriers in radiative recombination of excess electron-hole pairs.

response to photons and high energy particles. 3. The photocurrent in the external

circuit is proportional to the intensity of the incident radiation.