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for jee and boards > PHYSICS VIVA > Flashcards

PHYSICS VIVA Flashcards

1
Q

state ohm’s law

A

ohm’s law states that the eletric current I flowing through a conductor is directlyproportional to the potential difference V across its end provideed the physical condition like temperature pressure and dimension of the conductor remains same

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2
Q

give mathmatical form of ohm’s law

A

V=IR

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3
Q

what are ohmic devices

A

devices which obey ohms law are called ohmic devices
ex-metals like Cu,Al,Ag

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4
Q

what are non ohmic devices

A

devices which are do not obey ohm’s law are called non ohmic devices
ex- diodes,transistors,vaccume tubes

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5
Q

what is effect of temperature on the resistance of a conductor

A

increases with increase in the temperature

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6
Q

+how do u conclude that the conductor used in a conductor obeyed ohm’s law

A

it is done by 2 methods
- the ration of volt meter reading and the corresponding ammeter reading comes to constant
- a graph btw v and i comes to a staight line

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7
Q

what are the factors affecting the resistance

A

length area of crosssection nature of material and temperature of conductance

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8
Q

define resistance

A

opposition offered by the material of wire to the flow of the current
R=I/V

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9
Q

define the unit of resiistance

A

1 ohm=1v/1A
the si unit of resistance is ohm
1ohm is the resistance of a conductor carrying current of one apere when potential difference is mainrained across its ends

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10
Q

what is the cause of the resistance

A

collision of drifting electrons

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11
Q

what is the function of a rheostat

A

it is a variable resistance resistance and is commnly used for adjusting the strength of eletric current

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12
Q

what is conductance

A

the reciprocal of resistance is called conductance. denoted by G
G=1/R

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13
Q

what does the slope of V-I graph reprents

A

resistance

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13
Q

define resistivity or specific resistance of the material of conductance

A

resistance of a conductor of unit length and unit cross sectional area
unit is ohm meter

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14
Q

define eletrical conductivity

A

reciprocal of resistance
represented by the symbol sigma=1/ro

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15
Q

what is wheat stone bridge

A

it is the arrangement of the 4 resistors in quadrilateral form to find the unknown resistance of the 4th resistor by the other 3 resistors

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16
Q

what is meter bridge

A

it is the practical form of wheatstone bridge
it is used to determice the reistance and resistivity of a alloy wire

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17
Q

whenis a wheatstone bridge is said to be balanced

A

when no current flows through the galvanometer and it giives zero deflection

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18
Q

what is the condition for a wheatstone bridge to be balanced

A

p/q=r/s

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19
Q

what is balancing length

A

it is length of the bridge wire for which trhe deflection shows zero deflection

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20
Q

what is null point

A

it is a point on the wire, keeping jockey at which the galvanometer gives zero deflection

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21
Q

how does resistiviity of the conductor vary with length and area of cross section of the conductor

A

it is independet of length and area of cross section of the conductor

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22
Q

when are the resitors are said to be connected in series

A

when they are connected in series and coneected in end end to manner so that the current flow is same through out the same

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23
Q

when does the resistors are said to be connected in parallel combination

A

when they are connected in a common pointg so that the pd is same

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24
Q

when 2 reisitors are connected in seires the equivalent resistance is

A

Rs=R1+R2

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25
Q

when 2 resistance is connected in paralle lwhat is the equivalent series

A

I/Rp=1/R1+1/R2
=> 1/Rp=(R1+R2)/(R1R2)

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25
Q

what heppens to the equivalent reisitance when the resistors are connected in seires

A

equivalent resistance will be than greater resistance

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26
Q

what happens to the equivalent resistoer when connected in parallel

A

equivalent resistance will be lesser than the least resistance

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27
Q

what is internal resistance of a cell

A

the opposition offered by the cell itself to flow the current

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28
Q

what is the internal resistance of an ideal cell

A

zero

29
Q

what are the factors on which the internal resistance of a cell depends

A
  1. distance btw the electordes
  2. facing surface area
    3.nature of electrode
    4.internal resistance of the cell
30
Q

does internal resistance of the cell depends on the external resistance connected

A

no

31
Q

what is galvanometer

A

device used to detect feeble eletric current in the circuits

32
Q

why divisions of a galvanometer scale are equally spread

A

the deflection of a needle is directly proportional to the current
IαΘ

32
Q

define figure of merit of a galvanometer

A

the quantity oof current required to produce a deflection of one division in the galvanometer is callled figure of merit of the galvanometer
represented by k

33
Q

define current sensivity

A

the deflection produced in the galvanometer when 1 unit of current is passed through it

34
Q

what do u mean by resistance of a galvanometer

A

the resistance of the coil of a galvanometer
denoted by G

34
Q

why is this method called half deflection method

A

cause the deflection is made half by the shumt resistor

35
Q

what is there zener diode

A

PN junction diode

36
Q

mention any one applicaton of zener diode

A

voltage regulator

37
Q

zener breakdown voltage

A

the voltage becomes constant and current increases

38
Q

what iis voltage regulator

A

it is a device which produce a constant output voltaGE irrsepective of variation in the voltage

39
Q

what is zener current

A

the reverse current after breakdown

40
Q

what is voltmeter

A

a device measured for measuring eletric potential difference btw 2 points in a circuit

41
Q

required properties for a volt meter

A

must have a large resistance and less current carrying capacity

42
Q

why should a voltmeter have a very large resistance

A

when connected in parallel in circuit iit should not divert much current from parallel branch

43
Q

why is galvanometer not suitable to work asvoltmeter

A

galvanomter has less resistance and more current carrying capacity is required

44
Q

how is a galvanomter converted into a voltmeter

A

by connecting a high resistance in series with the galvanometer coil

45
Q

how the high resistance in series gives required properties to the galvanometer

A

increases the overall resistance og the voltmeter and decreases its current carrying capacity

46
Q

what is shunt ?its Si unit

A

small resistance connected in a parralel with the galvanometer
Si unit is ohm

47
Q

how is voltmeter to be connected in a circuit

A

connected in parallel with the circuit element across which the pd to measured

48
Q

what is a resistance of a ideal voltmetr

A

infinite ∞

49
Q

what is AC

A

current changes every instant of time and direction changes periodically

50
Q

what is the unit of frequency of AC

A

hertz Hz
per second

51
Q

what is resonance

A

when the natural frequency of a partical is equal to the frequency of driving force then resonance takes place

52
Q

when will wire resonate

A

the frequency of AC source is equal to the natural frequency of the vibration of the wire

53
Q

what is resonating length

A

the distance btw 2 knife edges when resonance takes place

54
Q

what iisan electromagnet

A

device which gets magnet when current is passed through it

55
Q

how is the frequency of electromagnet related with the frequency of the alternating current which magnetise it

A

it is twice the frequecny of AC

56
Q

what is natural frequency of the sonometer wire

A

f=1/2L(√T/µ)
where,
µ= linear mass density
T= tension in the wire
L=length of the wire

57
Q

what are stationary waves

A

when 2 identical waves moving in same frequency and amplitude ina medium with the same speed but in opposite direction

58
Q

what are nodes and antinodes

A

nodes are point of zero amplitude and antinodes are points of maximum amplitude

59
Q

define a spherical lens

A

a piece of transparent medim bounded by at least one spherical surface

60
Q

describe different types of lenses

A

(i)convex lens and (ii)concave lens
(i) thick in middle and thin in outside
(ii)thin in middle and thick in outside

61
Q

define apertus of a lens

A

the diameter of the circular edge of the lens is called the aperture of the lens

62
Q

define optical centre of a lens

A

it is a fixed poinmt inside the lens on its principal axis through which the light passes undeviated

63
Q

what is the type of a eye lens

A

eye lens is convex

64
Q

can u find the focal length of a concave lens by distant object method

A

no because it does not form a real image to be obtained on a screen

65
Q

what is the focal length of a lens

A

distance btw optical centre and the principal focus of a lens Si unit is meter

66
Q

what are the practical use of lens

A

spectacles,microscope,telescope,other optical uses

67
Q

define SI unit of power

A

diopter is SI unit of power
one diopter is the power of lens whose focal length is one mete

67
Q

what are the sign for the power of a convex lens and concave lens

A

concave lens- +ve and focal lengthis +ve
convex lens- -ve and focal length is -ve

68
Q

on what factors do focal length of convex lens depends

A
  • radii of curvature of lens
  • refractive index of lens
  • refractive index of surrounding medium
    -wavelength of light used
69
Q

what is lens maker formula

A

it is the relkation btw focal length and radii of curvature refractive index ofthe material of lens and refractive index of surroundings

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