Luminous Intensity

Q. Candela is the SI unit of:

1. Force
2. Luminous intensity
3. Power
4. Electric current

Q.

The amount of light received per unit area from a source of light is called:

1. Luminosity of light

2. Force of light

3. Intensity of light

4. Both (A) and (C)

Q.

Two coherent monochromatic light beams of intensities $4I$ and $9I$ are superimposed. The maximum and minimum possible intensities in the resulting beam are

1. $3I$ and $2I$

2. $9I$ and $5I$

3. $16I$ and $3I$

4. $25I$ and $I$

Q.

The SI unit of luminous intensity is

1. ampere

2. candela

3. mole

4. none of these

Q.

Kelvin is the fundamental unit of the luminosity of a source in S.I.

1. True
2. False

Q. If the luminous intensity of a unidirectional bulb is 100 candela then total luminous flux emitted from the bulb is.

1. 1256 lumen
2. 1561 lumen
3. 985 lumen
4. 961 lumen

Q. If luminous intensity of a unidirectional bulb is 100 candela then total luminous flux emitted from the bulb is?

Q. The distance between a point source of light and a screen is doubled. The intensity will be

1. four times the original value
2. two times the original value
3. half the original value
4. one quarter of the original value

Q. Candela is a unit of

1. accoustic intensity
2. electric intensity
3. luminous intensity
4. magnetic intensity

Q. The intensity produced by a long cylindrical light source at a small distance $r$ from the source is proportional to

1. $\frac{1}{r}$
2. $\frac{1}{r^3}$
3. $\frac{1}{r^2}$
4. None of these

Q. Luminous flux and luminous intensity are related as

1. $\varphi =4\pi I$
2. $\varphi =\frac{1}{4\pi }$
3. $\varphi =\frac{4\pi }{I}$
4. $I=4\pi \varphi$

Q. Label the parts for a lighted bulb in the given diagram.

1. Light source
2. Solid angle
3. Surface area

Q. Figure shows a glowing mercury tube. The intensities at point $A,B$ and $C$ are related as

1. $B>C>A$
2. $A>C>B$
3. $B=C>A$
4. $B=C<A$

Q. A 100 W lamp is rated 0.8W per candela; the luminous flux of the source is nearly :

1. $1481.6lm$
2. $1603.4lm$
3. $1501.3lm$
4. $1571.4lm$

Q. SI unit of Luminous Intensity is _______.

1. Ampere
2. Kelvin
3. Celsius
4. Candela

Q. A lamp is hanging at a height of $40m$ from the centre of a table. If its height is increased by $10cm$, the illuminance on the table will decrease by

1. $10$%
2. $20$%
3. $27$%
4. $36$%

Q.

Arrange $\mathrm{\alpha },\mathrm{\beta }\mathrm{and}\mathrm{\gamma }$ rays in ascending order with respect to their Penetrating power.

Q. A source emits $31.4$ $W$ of radiant flux distributed uniformly in all directions. The luminous efficiency is $60lumen/W$. Find the luminous intensity of the source.

1. $600$ $\pi$$Cd$
2. $600$ $Cd$
3. $100$ $Cd$
4. $150$ $Cd$

Q. A source of light emits a continuous stream of light energy which falls on a given area. Luminous intensity is defined as

1. luminous energy emitted by the source per second
2. luminous flux emitted by the source per unit solid angle
3. luminous flux falling per unit area of a given surface
4. luminous flux coming per unit area of an illuminated surface

Q. A circular area of radius $1cm$ is placed $2m$ away from a point source. The source emits light uniformly in all directions. The source is on the line of the normal from the centre of the area. $2\times {10}^{-3}$luminous flux is incident on the area. Find the total flux emitted by the source.

1. $320lm$
2. $355lm$
3. $285lm$
4. $250lm$

Q. A screen recieves $3$ watt of radiant flux of wavelength $6000$ $\mathring{A}$. One lumen is equivalent to $1.5\times {10}^{-3}$ watt of monochromatic light of wavelength $5500$ $\mathring{A}$ is $1.00$, then the luminous flux of the source is ___

1. $4\times {10}^3$ $lm$
2. $3\times {10}^3$ $lm$
3. $2\times {10}^3$ $lm$
4. $1.37\times {10}^3$ $lm$

Q. A student is studying a book placed at the edge of a circular table of radius $R$. A point source of light is suspended directly above the centre of the table. What should be the height of the lamp so that maximum illuminance is produced at the position of the book?

1. $R$
2. $\frac{R}{2}$
3. $\frac{R}{\sqrt{2}}$
4. $\frac{R}{\sqrt{3}}$

Q. A lamp of luminous intensity $20$ $Cd$ is hanging at a height of $40$ $cm$ from the center of a square table of side $60$ $cm$. The illuminance at the midpoint of the side of the table will be

1. $32$ lux
2. $125$ lux
3. $100$ lux
4. $64$ lux

Q. Will the gausss law be applicable if it would have not followed the inverse square law?

Q. A point source emitting uniformly in all directions is placed 0.5 m above a table top. The luminous flux of the source is $500$ $\pi$ lumen. Find the illumnance at a small surface area of the table top 0.8 m from the source

1. $118lux$
2. $125lux$
3. $115lux$
4. $122lux$

Q. 35. The second overtone of a closed pipeand the third overtone of an open pipeare in unison. The ratio of their funda-mental frequencies are(a) 5:4(c) 25: 16(b) 4:5(d) 16:25

Q. In youngs double slit experiment, the ratio of maximum to minimum intensities of the fringe system is 4:1. The amplitudes of the coherent sources are in the ratio
A] 4:1 B] 3:1 C] 2:1 D] 1:1

Q. A room is illuminated by an extended source. The illuminance at a particular portion of a wall can be increased by

1. Moving the source
2. rotating the source
3. bringing some mirrors in proper positions
4. changing the colour of the source

Q. The luminous intensity of 100 W unidirectional bulb is 100 candela. The total luminous flux emitted from bulb will be

1. $400\pi$ lumen
2. $200\pi$ lumen
3. $100\pi$ lumen
4. $300\pi$ lumen

Q. The luminous efficiency of a lamp is $8.8$ lumen/watt and its luminous intensity is $700Cd$. The power of the lamp will be

1. ${10}^1$ $W$
2. ${10}^4$ $W$
3. ${10}^2$ $W$
4. ${10}^3$ $W$