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Number of electrons emitted by a surface exposed to light is directly proportional to
Key Idea Number of photoelectrons emitted proportional to intensity of incident light.
For a given metal, rate of emission of photo electrons i.e., photocurrent is directly proportional to the intensity of incident radiation for a given light i.e., a bright light always gives more photocurrent than a dim one for a given frequency.
Intensity here means energy incident normally per unit area per second and is also called, energy flux or power density.
In photoelectric emission the number of electrons ejected per second
For a fixed frequency of incident radiation, the number of electron ejected per second increases linearly with increase in intensity of incident light.
A travelling microscope is held vertical and focussed at a point object 'O'. The reading of the microscope is 9.65 cm. A thick glass slab is placed on O and its image O’ was observed with the microscope by refocusing it. The reading was now 11.65 cm. Finally a few particles of lycopodium powder is sprinkled on the top of the glass slab and it is viewed with the microscope by refocusing. The reading of microscope is found to be 12.85 cm. The refractive index of the material of the glass slab is
According to Hooke's law of elasticity, if stress is increased, the ratio of stress to strain
Young's modulus (Y), the ratio of stress to strain ,remains constant for a particular material. i.e.
Y= stress/ strain=constant
A stepup transformer operates on a 230 V line and supplies a load of 2 ampere. The ratio of the primary and secondary windings is 1 : 25. The current in the primary is
If the distance between the plates of parallel plate capacitor is halved and the dielectric constant of dielectric is doubled, then its capacity will
Two thin wire rings each having a radius R are placed at a distance d apart with their axes coinciding. The charges on the two rings are +q and q. The potential difference between the centres of the two rings is
Figure shows the two ring 1 and 2 each of radius R and having charges +q and −q
Let A and B be the centers of the two rings and VA and VB be the respective potentials at these points, then
VA= Potential due to ring 1+ Potential due to ring 2
Therefore potential difference between the two rings,
A mass of a gas exerts a pressure of 72 cm of mercury at 27^{o} cm of mercury at 27^{o}C. It is heated at constant volume and the pressure after some time becomes 90 cm of mercury. What is the temperature of the gas?
(P_{1}/T_{1})=(P_{2}/T_{2})
T_{2}=(P_{2}.T_{1})/P_{1}
T_{2}=(90x300)/72
T_{2}=375 K
T_{2}=375273 = 102^{o}C
The mass of the earth is 81 times that of the moon and the radius of earth is 3.5 times that of the moon. The ratio of the acceleration due to gravity at the surface of the moon to that at the surface of the earth is
A particle moves in a circular orbit under the action of a central attractive force inversely proportional to the distance 'r'. The speed of the particle is
We know that the centripetal force F = k/r
For some constant k and radius of curvature r.
Also we know centripetal force F = mv^{2} /r
Thus we get v = √k/m.
A nucleus with Z = 92 emits the following in sequence: α , α , β^{−} , β^{−} , α , α , α , α ; β^{−} , β^{−} , α , β^{+} , β^{+} , α . The Z of the resulting nucleus is
In the following question, a Statement of Assertion (A) is given followed by a corresponding Reason (R) just below it. Read the Statements carefully and mark the correct answer
Assertion(A): Virtual images are always erect.
Reason (R): Virtual images are formed by diverging lenses only.
The virtual image is always erect. The common example of virtual image is the image formed in the mirror when we stand in front of that mirror. A real image is that image which is formed when the light rays coming from an object actually meet each other after reflection or refraction.
In the following question, a Statement of Assertion (A) is given followed by a corresponding Reason (R) just below it. Read the Statements carefully and mark the correct answer
Assertion(A): According to law of conservation of mechanical energy sum of kinetic energy and potential energy is always constant.
Reason(R): Mechanical energy is conserve.
Conservation of Mechanical Energy
The sum total of an object’s kinetic and potential energy at any given point in time is its total mechanical energy. The law of conservation of energy says “Energy can neither be created nor be destroyed.”
So, it means, that, under a conservative force, the sum total of an object’s kinetic and potential energies remains constant.
When seen in green light, the saffron and green portions of our National Flag will appear to be
When seen in green light, the saffron and green portion of our national Flag will appear to be black and green respectively, because saffron absorbs the green light completely without any reflection so is shown as black, but Green portion of the Indian national flag reflects the same green light which falls on it so it appear as green in colour only.
The density of dry air is more than the moist air. When moisture is removed from air, its density increases. The speed of sound in a medium is inversely proportional to the square root of its density. Therefore, the speed of sound in moist air is more than that in dry air. Hence, correct answer is (D).
Heat capacity of a substance is infinite. It means
Specific heat is defined as amount of joules to make 1 gram of a substance to change the temperature by 1 celsius; if the specific heat is infinite, that means it takes infinite amount of joules to change temperature, thus no change in temperature takes place even if you add or subtract heat because it would take infinite energy to change the temperature.
Two tuning forks A and B produce 6 beats per second when sounded together. When B is slightly loaded with wax, the beats are reduced to 4 per second. If the frequency of A is 512 Hz, the frequency of 'B' is
When loaded with wax, frequency of beats is reduced.
⇒ Frequency of B is higher than that of A.
⇒f_{B}−f_{A}=6
⇒f_{B}=(512+6)=518 Hz
The K.E. of a light and a heavy object is same Which object has more momentum?
In Young's double slit experiment, an interference pattern is obtained on a screen by a light of wavelength 6000 Å coming from the coherent sources S_{1} and S_{2}. At certain point P on the screen third dark fringe is formed. Then the path difference S_{1}p − S_{2}p in microns is
For dark fringe at P S_{1}p − S_{2}p =Δ=(2n−1)λ/2
Here n =3 and l = 6000
So, =15000AA = 1.5 micron
Two rods 1 and 2 are released from rest as shown in figure.
Given: l_{1}=4l, m_{1}=2m, l_{2 }= 2l and m_{2 }= ml_{1}=4l, m_{1}=2m,l_{2}=2l and m_{2}=m. There is no friction between the two rods. If αα be the angular acceleration of rod 1 just after the rods are released. Then :
Q. What is the normal reaction between the two rods at this instant ?
At what speed a ball must be projected vertically upward so that distance travelled by it in 5^{th} second is equal to distance travelled in sixth second (in m/s):
time of flight = (5 sec) × 2 = 10 sec
µ = gt = 9.8 × 5 = 49 m/s
In thermodynamic process pressure of a fixed mass of gas is changed in such a manner that the gas releases 30 joule of heat and 18 joule of work was done on the gas. If the initial internal energy of the gas was 60 joule, then, the final internal energy (in J) will be:
ΔQ = –30J
Δw = –18
U_{i} = 60 J
U_{f} = ?
ΔQ = Δw + U_{f} – U_{i}
–30 = –18 + U_{f} – 60 ⇒ U_{f} = 48 J
In a certain amplitude modulate wave, maximum amplitude is 8V. If modulation factor is 60% then minimum amplitude of the wave, will be
Figure shows a Meter bridge wire AC has uniform crosssection. The length of wire AC is 100 cm. X is a standard resistor of 4Ω and Y is a coil. When Y is immersed in melting ice the null point is at 40 cm from point A. When the coil Y is heated to 100ºC, a 12Ω resistor has to be connected in parallel with Y in order to keep the bridge balanced at the same point. The temperature coefficient of resistance of the coil is x × 10^{–2} SI units. Find the value of x.
This is linear variation of resistance.
12 = 6 (1 + α 100)
α = 1 × 10^{–2}
x = 1
Two cars moving in opposite directions approach each other with speed of 22 m/s and 16.5 m/s respectively. The driver of the first car blows a horn having a frequency 400 Hz. The frequency heard by the driver of the second car is [velocity of sound 340 m/s] (in Hz):
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