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37901.

Choose the wrong statement about equipotential surfaces.

Answer»

It is a surface over which the potential is constant
The ELECTRIC FIELD is parallel to the equipotential surface
The electric field is PERPENDICULAR to the equipotential surface
The electric field is in the direction of steepest decrease of potential

Answer :B
Discussion
37902.

The frequency of ac is doubled . What happens to the resistance, inductive reactance and capacitive reactance ?

Answer»

SOLUTION :R remains the same.
Induvtive REACTANCE `X_L=L_omega` gets doubled.
Capacitative reactance `X_L-1/C_omega` is HALVED.
Discussion
37903.

An observer measures speed of light to be C, when he is stationary with respect to the source. If the observer moves with velocity V towards the source then the velocity of light observed will be

Answer»

C-V
C +V
`SQRT(1-V^(2)/C^(2))`
C

Answer :D
Discussion
37904.

A sound waves vibrates according to the equation phi=0.03sinpit. It sends out waves of velocity 1.5 m/s and T=2 sec. The wavelength of sound is

Answer»

6 m
4.5 m
3 m
2.5 m

Answer :C
Discussion
37905.

The dimensional formula of latent heat is :

Answer»

`M^(0)L^(2)T^(-2)`
`ML^(2)T^(-1)`
`MLT^(-1)`
`M^(0)L^(2)T^(-1)`

Solution :Latent heat `=("heat energy")/("mass")`
`=(ML^(2)T^(-2))/(M)=[M^(0)L^(2)T^(-2)]` which is CHOICE `(a)`.
Discussion
37906.

Surface of Earth is considered at ...... gravitational potential (in practice).

Answer»

infinite
negative
positive
zero

SOLUTION :In PRACTICE ABSOLUTE value of gravitational potential is not important, but CHANGE in potential Is important. Hence, any value of gravitational potential can be considered on the surface of EARTH. But in practice, in order to have ease in the calculations, we prefer to select the value of gravitational potential on the surface of Earth to be zero.
Discussion
37907.

(A) : The ion cannot move with a speed beyond a certain limit in a cyclotron. (R) : As velocity increases the mass of ion increases.

Answer»

Both 'A' and 'R' are TRUE and 'R' is the correct explanation of 'A'.
Both 'A' and 'R' are true and 'R' is not the correct explanation of 'A'
'A' is true and 'R' is FALSE
'A' is false and 'R' is false

Answer :A
Discussion
37908.

Two convex lesses of power 2 D and 5 D are separated by a distance 1/3m m The power of the optical system formed is

Answer»

`+2D`
`-2D`
`-3D`
`+3D`

ANSWER :D
Discussion
37909.

The maximum kinetic energy of emitted photoelectrons depends on

Answer»

POTENTIAL
FREQUENCY
incident ANGLE
pressure

Solution :Frequency
Discussion
37910.

For common emitter configuration, if alpha and beta have their usual meanings, the incorrect relationship between alpha and beta is :

Answer»

`(1)/(alpha)=(1)/(BETA)+1`
`alpha=(beta)/(1-beta)`
`alpha=(beta)/(1+beta)`
`alpha=(beta^(2))/(1+beta^(2))`

SOLUTION :`(B) alpha=(beta)/(1-beta) (D) alpha=(beta^(2))/(1+beta^(2))`
For transistor `I_(E )=I_(B)+I_(C )`
`THEREFORE (I_(B))/(I_(C ))=(I_(B))/(I_(C ))+1`
`therefore (1)/(alpha)=(1)/(beta)+1""`(Option (A) is correct)
`therefore (1)/(alpha)=(1+beta)/(beta)`
`therefore alpha=(beta)/(1+beta)""` (Option C is correct)
`therefore` Option (B) and (D) are not correct.
Discussion
37911.

If vectors vecA and vecB are 3hati - 4hatj + 5hatk and 2hati + 3hatj -4hatk respectively then find the unit vector parallel to vecA+vecB

Answer»

`((5i-j+k))/(SQRT(27))`
`((5i+j+k))/(sqrt(27))`
`((5i+j+k))/(27)`
`((5i-j-k))/(27)`

ANSWER :A
Discussion
37912.

The opposition to the flow of electricity by a wire wound over a wooden cylinder having large no of turns what we call ?

Answer»

SOLUTION :Inducative REACTANCE
Discussion
37913.

A capacitor is an electronic component having two conductors separated by an insulators .An insulated capacitor with air between plates has a potential of V_0and a charge Q_0.When the space between plates is filled with oil the potential difference becomes V and charge becomes Q.Which of the followingrelation is correct?

Answer»

`Q=Q_0,Vgt_0V_0`
`Q=Q_0,VltV_0`
`QgtQ_0,V=V_0`
`Q=Q_0, V=V_0`

ANSWER :B
Discussion
37914.

(a) Six equal charges have been placed at the vertices of a regular hexagon. Charge at vertex A is moved to the centre of the hexagon and there it experiences a net electrostatic force of magnitude F. Charge at E is also moved to the centre so as to double the magnitude of the charge at the centre. Calculate the magnitude of the electrostatic force that this central charge experiences now. (b) Three charges of equal magnitude lie on the vertices of an equilateral triangle ABC. All of them are released simultaneously. The charge at A experiences initial acceleration along AD where D is the midpoint of the side BC. Find the direction of initial acceleration of the charge at B.

Answer»


Answer :(a). 2F towards POINT F
(B). In a DIRECTION making an angle of `60^(@)` with BA (NOT along BC).
Discussion
37915.

Two radioactive substances X and Y initially contain equal number of atoms . Their half-lives are 1 hour and 2 hours respectively . Calculate the ratio of their rates of disintegrations after four hours.

Answer»

Solution :Rate of disintegration
`(R),(DN)/(dt)= lamdaN = N XX (0.693)/T`
`:.` The ratio of rates disintegration , `R_1/R_2=(N_1/N_2)T_2/T_1`
Here , `T_(1) = 1 ` hour : `T_2` = 2 hours
`N_0` is same for both radio active substances. In four hours , X completes 4 half - lives as its half - life is 1 hour. The REMAINING number of ATOMS of X,
`N_(1)= N_0/(2^n)= N_0/(2^4) = N_0/16` . Y completes 2 half - lives in four hours as its half - life 2 hours.
The number of atoms of Y remaining .
`N_2=N_0/2^2=N_0/4"" :. R_1/R_2=N_0/16xx4/N_0(2/1)=1/2`
Discussion
37916.

An equilateral prism is made up of material of refractive index sqrt3. The angle of minimum deviation of light passing through the prism is ________.

Answer»


SOLUTION :HINT `n=SQRT3=(SIN""(A+D_(m))/(2))/(sin""(A)/(2))=(sin""(60^(@)+D_(m))/(2))/(sin 30^(@))`
`rArr sin((60^(@)+D_(m))/(2))=sqrt3.sin30^(@)=(sqrt3)/(2) or (60^(@)+D_(m))/(2)=sin^(-1)((sqrt3)/(2))=60^(@)`
`rArr D_(m)=60^(@)`
Discussion
37917.

Two polarising sheets have their polarising directions parallel to each other such that the intensity of the transmitted light is maximum. Through what angle must either sheet be turned so that the intensity becomes one-half the initial value ?

Answer»

`30^(@)`
`45^(@)`
`135^(@)`
Both (2) and (3) are correct

Answer :D
Discussion
37918.

A transverse wave is represented by the equation y = y_(0) (2pi)/(lambda)sin (vt - x). For what value of lambda is the particle velocity equal to two times the wave velocity ?

Answer»

`lambda = 2 PI y_(0)`
`lambda = 2 pi y_(0)` /3
`lambda = 2pi y_(0)` /2
`lambda = 2 pi y_(0)`.

Solution :PARTICLE vel. = `(DY)/(DT) = (2 pi)/(lambda) vy_(0)`
Now `(2pi)/(lambda) vy_(0) = 2v`
or `lambda = pi y_(0)`
CORRECT choice is (D).
Discussion
37919.

The equations of the wave travelling in a medium is Y=5cospi(100t-x). What is the wavelength of the wave ?

Answer»

Solution :The given equation is y = 5 `cospi(100t - x)`
y = 5 `cos(100pit - PIX)`
STANDARD equn is y = a cos(WT + KX)
where k = `(2PI)/lamda` Comparing k = `(2pi)/lamda` = 2units.
Discussion
37920.

In the above question, if the balancing length for a cell of emf E is 60 cm, the value of E will be

Answer»

`3 MV`
`5 mV`
`6 mV`
`2000 mV`

Solution :The VALUE of `E =` POTENTIAL gradient` xx` Length
`= (5 mVm^(-1)) (60 cm) = 3 mV`
Discussion
37921.

A gun weighing 100 kg is used to fire an iron ball weigh ing 1 kg horizontally from a cliff of height 500 m above the ground. The ball falls 400 m away from the bottom of the cliff. What is the recoil velocity of the gun? (Take g =10 ms^(-2))

Answer»

`0.8 MS^(-1)`
`0.4 ms^( -1)`
`1.2 ms^(-1)`
`0.2 ms^(-1)`

Solution :Here `H=(1)/(2)g t^ (2)`

`:.t^(2)=(2h)/(g)=(2xx500)/(10)`
`t=10 SEC`
Also `x=ut`
`:.u=(x)/(t)=(400)/(10)`
`=40 m sec^(-1)`
Now recoil velocity `V=(mu)/(M)`
`V=(1xx40)/(100)=0.4 ms^(-1)`
Hence (b) is the right CHOICE
Discussion
37922.

Assertion : A transistor amplifier operates in active region. Reason : In active region transistor characteristic is liner.

Answer»

If both assertion and REASON are TRUE and the reason is the correct explanation of the assertion
If both assertion and reason are true but the reason is not the correct explanation of the assertion
If assertio is true statement but reason is false.
If both assertion and reason are false statement

Solution :In active region collector junction is reverse BIASED and emitter junction is FORWARD biased. In this region transistor current responds most sensitively to bae current. If transistor is to be USED as an amplifier, it must operate in this region.
Discussion
37923.

A short conductor of length 4 cm placed parallel to a long conductor of length 2 m near its centre. The conductors carry current of 2 and 5A respectively in opposite directions. What is the total force experienced by the long conductor when they are 2cm apart?

Answer»

SOLUTION :`4 XX 10^(-6)` N
Discussion
37924.

A conducting gas is in the form of a long length of the cylinder. The current is distributed uniformly across the cross - section of the gas. Disgard thermal and electrostatic forces among the gas molecules. Due to the magnetic fields set up inside the gas and the forces which they exert on the moving ions, the gas will tend to

Answer»

expand
Contract
expand and contract alternately
none of the above

Solution :TREAT the gas as a thick conductor carrying a uniform current. Apply Ampere's law to find the magnetic FIELD. Then apply the left`-` HAND RULE to find the direction of the Ampere FORCE.
Discussion
37925.

In the shown network, charge on 2muF state would be

Answer»

`10 MUC`
`20 muC`
`5mu C`
 `40 muC`

ANSWER :A
Discussion
37926.

Complete the line True equality is equal to

Answer»

TRUE wisdom
True inter-dimensional warfare
True script
None of the above

Answer :A
Discussion
37927.

An electron (of mass m) and a photon have the same energy E in the range of few eV.The ratio of the de-Broglie wavelength associated with the electron and the wavelength of the photon is (c=speed of light in vaccum)

Answer»

`(1)/(c)((E )/(2M))^((1)/(2))`
`c((E )/(2m))^((1)/(2))`
`sqrt(2ME)/(c )`
`((E )/(2m))^((1)/(2))`

Solution :de-Broglie wavelength of ELECTRON `lambda_(c)=(h)/(sqrt(2mE))`
de-Broglie wavelength of photon
`lambda_(p)=(hc)/(E )[because E =(hc)/(lambda)]`
`THEREFORE` Ratio `(lambda_(c))/(lambda_(p))=(h)/(sqrt(2mE))xx(E )/(hc)`
`=(1)/(2)(sqrt(E )/(2m))=(1)/(c )((E )/(2m))^((1)/(2))`
Discussion
37928.

What is the dimension of magnetic flux ?

Answer»

SOLUTION :`M^1L^2T^(-2)A^(-1)`
Discussion
37929.

The electron drift speed is estimated to be only a few mm s^(-1)for currents in the range of a few amperes. How then is current established almost the instant a circuit is closed ?

Answer»

Solution :Electric FIELD is established throughout the circuit almost instantly (with the speed of light)causing at every point a LOCAL ELECTRON drift. Establishment of a current does not have to wait for ELECTRONS from one end of the conductor travelling to the other end. However, it does take a little while for the current to REACH its steady value.
Discussion
37930.

Alternating current cannot be measured by a d.c. ammeter because

Answer»

a.c. cannot pass through d.c. AMMETER.
a.c. changes its DIRECTION.
average value of a.c. for complete cycle is ZERO.
a.c. is virtual

Solution :Alternating CURRENT cannot be MEASURED by a d.c. ammeter because average value of an a.c. for a complete cycle is zero.
Discussion
37931.

A battery consists of a variable number n of identical cells having internal resistance connected in series. The terminals of the battery are short circuited and the current I measured. Which one of the graph below shows the relationship between I and n?

Answer»




ANSWER :D
Discussion
37932.

A body moves with uniform acceleration. If v_(1), v_(2) and v_(3) be the average velocities in three successive intervals of time t_(1), t_(2) and t_(3), then :

Answer»

`v_(1)-v_(2) :v_(2)-v_(3)=t_(1)-t_(2):t_(2)+t_(3)`
`v_(1)-v_(2) :v_(2)-v_(3)=t_(1)+t_(2):t_(2)+t_(3)`
`v_(1)-v_(2) :v_(2)-v_(3)=t_(1)+t_(2):t_(1)-t_(3)`
`v_(1)-v_(2) :v_(2)-v_(3)=t_(1)+t_(2):t_(2)-t_(3)`

ANSWER :B
Discussion
37933.

The power factor for a purely capacitive circuit is

Answer»

1
`SQRT(2)`
`(1)/(sqrt(2))`
Zero

Answer :A
Discussion
37934.

A charged particle is projected perpendicular to uniform magnetic field. It describes a circle, the quantities which are inversely proportional to specific charge are i) Radius ii) K. E iii) Time period iv) Momentum

Answer»

Only i&II are true
Only i,ii&IV are true
Only ii & III are true
Only i & iii are true

Answer :D
Discussion
37935.

A radio can tune over the frequency range of a portion of MW broadcast band: (800 kHz to 1200 kHz). If its LC circuit has an effective inductance of 200 muH, what must be the range of its variable capacitor?

Answer»

Solution :`v=(1)/(2pi) sqrt((1)/(LC)), i.e., C=(1)/(4pi^(2)v^(2)L)`
For `L=200muH, v=1200kHz, C=87.9pF`.
For `L=200muH, v=800kHz, C=197.8pF`.
The variable CAPACITOR should have a RANGE of about 88 pF to 198 pF.
Discussion
37936.

The Balmer series for the H atom can be observed

Answer»

if we MEASURE the FREQUENCIES of light emittedwhen an excited atom FALLS to the ground state
if wemeasure the frequencies of light emitteddue to transition between excited states and the firstexcited state
in any transition in a H atom
as a sequence of frequencies with the higher frequencies getting closelypacked

Answer :B::D
Discussion
37937.

An YDSE is carried out in liquid of refractive index mu=1.3 and a thin film of air is formed in front of the lower slit as shown in the figure .If a maxima of third order id formedorder at the origin O, find thethickness of the air film . The wavelengthof light in air is lambda_(0)=0.78 mum and D/d = 1000 .

Answer»

`7.8 MU m`
`3.9 mu m`
`15.6 mu m`
`0.5 mu m`

ANSWER :A
Discussion
37938.

A and B are two points separately by a distance 5cm. Two charges 10 mu C and 20mu C are placed at A and B. The resultant electric intensity at a point P outside the charges at a distance 5cm from 10 mu C is

Answer»

`54 xx 10^(6) N//C` AWAY from `10 MU C`
`56 xx 10^(6)N//C` towards `10 mu C`
`9 xx 10^(6) N//C` away from `10 mu C`
zero

Answer :A
Discussion
37939.

The radiation used in the treatment of muscles ache is

Answer»

Infrared
Ultraviolet
Microwave
X-rays

Answer :A
Discussion
37940.

A string under a tension of 129.6 N produces 10 beats persecond when it is vibrated along with a tuning fork. When the tension in the string is increased to 160 N, it sounds in unison with the same tuning fork. Calculate the fundamental frequency oftuning fork. .

Answer»

Solution :Let n be the frequency of TURNING FORK. The frequency of string will be either (n+10) or (n - 10) As the tension in the string increase, its frequency INCREASES `(n infty sqrt(T))` and becomes n. This shows that the initial frequency (at = T = 129.6N) of string will be (n - 10). Hence
`n - 10 = (1)/(2L) sqrt(((129.6)/(mu)))`
`n = (1)/(2l) sqrt(((160)/(mu)))`
Dividingequation-(6.246)by equation-(6.247),weg
`(n - 10)/(n) = sqrt(((129.6)/(160)))`
Solving we get n = 100 Hz.
Discussion
37941.

In a Young's double slit experiment, 16th order maximum is obtained at a certain point on the screen with light of wavelength 6000overset@A. The order of the maximum obtained at the same point with light of wavelength 4800overset@A will be :

Answer»

16
10
20
8

Answer :C
Discussion
37942.

The mass number of a nucleus is

Answer»

ALWAYS less than its ATOMIC NUMBER
always more than its atomic number
EQUAL to its atomic number
some times more than and some times equal to atomic number

Answer :D
Discussion
37943.

Two short magnets of the same type, but of moments m and 2m are mounted on a frame so as to form a cross. If the combination is suspended at the centre with a vertical fibre, find the direction in which it will set in the earth's magnetic field. Calculate also the magnetic B-field at a distance d from the centre of the cross on the prolongation of one of the arms.

Answer»


Answer :`26^(@)36' (mu_(0))/(4PI) (2sqrt(2)m)/(d^(3)),(mu_(0))/(4pi) 6(msqrt(17))/(d^(3))`
Discussion
37944.

Assertion : When two semi conductor of p and n type are brought in contact, they form p-n junction which act like a rectifier. Reason : A rectifier is used to conventalternating currentinto direct current.

Answer»

Assertionis CORRECT, reason is correct, reason is a correct explanation for assertion.
Assertionis correct, reason is correct, reason is not a correct explanation for assertion
Assertionis correct, reasonis INCORRECT
Assertion is incorrect, reasonis correct

Solution :Study of junction diode CHARACTERISTICS shows that the junction diode offers a low resistance PATH, when forward biased and high resistance path when reverse biased. This FEATURE of the junction diode enables it tobeused as a rectifier.
Discussion
37945.

Where should a convex lens. of focal length 9 cm be placed (in cm) between two point sources S_1 and S_2which are 24 cm apart, so that images of both the sources are formed at the same place. You have to find distance of lens from S_1 or S_2 which ever is lesser.

Answer»


ANSWER :2
Discussion
37946.

The scientist who is credited with the discovery of 'nucleus' in an atom is

Answer»

J.J. Thomson
RUTHERFORD
Niels Bohr
Balmer

SOLUTION :Rutherford was credited with the discovery of nucleus at the CENTRE of atom BASED on his `alpha` - SCATTERING experiment observations.
Discussion
37947.

A fraction f_1 of a radioactive sample decays in one mean life, and a fraction f_2 decays in one half-life.

Answer»

`f_1 GT f_2`
`f_1 LT f_2`
`f_1=f_2`
May be (a), (b) or (C) depending on the values of the mean LIFE and half-life.

Answer :A
Discussion
37948.

Al0muF capacitor is connected to l00Vbattery. What is the electrostatic, energy stored ?

Answer»

SOLUTION :`C=10muF=10^-3F,V=100V`ELECTROSTATIC ENERGY stored `E=1/2CV^2=1/2(10^-5)xx(100)^2=6.05J`.
Discussion
37949.

A) It is possible to have mutual inductance without self-inductance B) If the current in an inductor is doubled, the stored energy in it is quadrupled C) One can have an inductance without a resistance

Answer»

A & B are false
B & C are false
A & C are false
All are false

Answer :C
Discussion
37950.

Explain effects of impurities on surface tension of a liquid?

Answer»

Solution :If organic SUBSTANCE is DISSOLVED in water than surface tension of water decreases because intermolecular forces decreases e.g. soap, phenol, Toothpaste etc.
If INORGANIC substance is dissolved in water then surface tension of water increases because intermolecular forces increases as inorganic substance forms ions when it is dissloved.
Discussion