Tag: measurements

Quizzes (29) Questions (59)

Questions Related to measurements

Multiple choice luminous intensity measurements physics

In the interference pattern, energy is

  1. created at the position of maxima

  2. destroyed at the positions of minima

  3. conserved but is redistributed

  4. not conserved
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

conserved but is redistributed

Multiple choice luminous intensity measurements physics

A lamp placed 60 cm from a screen produces the same illumination as a standard 100 W lamp placed 90 cm away on the other side of the screen. The luminous intensity of the first lamp is 

  1. $49.44W$
  2. $44.44W$
  3. $54.44W$
  4. $34.44W$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For same illumination $\dfrac{Power} { r^{2}}$ will be same


=> $\dfrac {100} { 0.9^{2}} = \dfrac {P} {0.6^{2}}$
=> P = $44.44 W$

Multiple choice luminous intensity measurements physics

Light has a wave nature, because-

  1. the light travel in a straight line

  2. Light exhibits phenomenon of reflection and refraction

  3. Light exhibits phenomenon interference

  4. Light exhibits phenomenon of photo electric effect.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Interference is a phenomenon unique to wave motion, where waves superimpose to form a resultant wave of greater, lower, or the same amplitude. Reflection and refraction can be explained by both wave and particle models, while the photoelectric effect supports the particle nature.

Multiple choice luminous intensity measurements physics

Light with energy flux 36$\mathrm { w } / \mathrm { cm } ^ { 2 }$ is incident on a well polished metal slate of side 2$\mathrm { cm }$ . Theforce experienced by it is

  1. 0.96$\mu N$
  2. 0.24$\mu N$
  3. 0.12$\mu N$
  4. 0.36$\mu N$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The force exerted by light on a surface is F = P/c, where P is the power (energy flux * area). For a perfectly reflecting surface, F = 2IA/c. For an absorbing surface, F = IA/c. Assuming absorption, F = (36 W/cm^2 * 4 cm^2) / (3 * 10^8 m/s) = 144 / 3 * 10^-8 N = 4.8 * 10^-7 N = 0.48 uN. If reflected, it is 0.96 uN. Given the answer 0.96 uN, the metal plate is considered a perfect reflector.

Multiple choice luminous intensity measurements physics

If relative luminosity is $0.65$ then the luminous flux of a $10 W$ source is

  1. $12130.6$
  2. $4125.5$
  3. $4352.5$
  4. $4452.5$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Luminous flux of a 10W source=Relative luminosity$\times$ luminous flux of 555nm source of 10W

=$0.65\times (685\times 10)=4452.5$

Multiple choice luminous intensity measurements physics

A battery operated torch is adjusted to give a parallel beam of light. It produces illuminance of 60 lux on a wall 2m away. The illuminance produced 3 m away is 

  1. $60$ lux
  2. $\displaystyle\ \frac{80}{3}$ lux
  3. $40$ lux

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since $\dfrac {dF}{dA}$ is a constant, where $F$ is the illuminance and $A$ is the area of cross section. Hence the illuminance produced 3 m away does not change and it is 60 lux.

Multiple choice luminous intensity measurements physics

Two coherent source must have the same :

  1. amplitude

  2. phase difference

  3. frequency

  4. both B and C
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Two coherent source have the same :

1) Frequency
2) Phase difference.

The correct option is D.

Multiple choice luminous intensity measurements physics

An electric lamp and a candle produce equal illuminance on a screen when placed $80 cm$ and $20 cm$ from the screen respectively. The lamp is now covered with a thin paper which transmit $49\%$ of the luminous flux. By what distance the lamp should be moved to balance the intensities at the screen again?

  1. $24 cm$
  2. $12 cm$
  3. $18 cm$
  4. $456 cm$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Case(i)
$\displaystyle\ \frac{I _{1}}{I _{2}}$ = $\displaystyle\ \left (\frac{80}{20} \right)^{2}$

Case(II)
$\displaystyle\ \frac{.49I _{1}}{I _{2}}$ =$\displaystyle\ \left(\frac{d}{20} \right)^{2}$

$d$ = $20\sqrt{.49(16)}$ = $20(2.8)$
 = $56$cm
Lamp be moved by $80$ - $56$ = $24$ cm

Multiple choice luminous intensity measurements physics

As the wavelength is increased from violet to red, the luminosity

  1. increases continuously

  2. decreases continuously

  3. first increases then decreases

  4. first decreases then increases
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The luminosity increases with increase in wavelenth, reaches a peak at around 550 nm then decreases.


Answer. C) first increases and then decreases. 

Multiple choice luminous intensity measurements physics

The parameter that determines the brightness of a light source sensed by an eye is 

  1. energy of light entering the eye per second

  2. wave length of the light

  3. total radiant flux entering the eye

  4. total luminous flux entering the eye
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The parameter that determines the brightness of a light source sensed by an eye is total luminous flux entering the eye.
$B = F$ where $B$ is the brightness and $F$ is the total flux entering the eye.