Subjective Type

In Figure, an isotropic point source of light S is positioned at distance d from a viewing screen A and the light intensity $$I_P$$ at point P (level with S) is measured. Then a plane mirror M is placed behind S at distance d. By how much is $$I_P$$ multiplied by the presence of the mirror?

Solution

The intensity of light from a point source varies as the inverse of the square of the
distance from the source. Before the mirror is in place, the intensity at the center of the
screen is given by $$I_P = A/d^2$$ , where A is a constant of proportionality. After the mirror is
in place, the light that goes directly to the screen contributes intensity $$I_P$$, as before.
Reflected light also reaches the screen. This light appears to come from the image of the
source, a distance d behind the mirror, and a distance 3d from the screen. Its contribution
to the intensity at the center of the screen is

$$I_r=\dfrac{A}{(3d)^2}=\dfrac{A}{9d^2}=\dfrac{I_p}{9}$$

The total intensity at the center of the screen is

$$I=I_p+I_r=I_p+\dfrac{I_p}{9}=\dfrac{10}{9}I_p$$

The ratio of the new intensity to the original intensity is $$I/I_P = 10/9 = 1.11$$.

SIMILAR QUESTIONS

Electromagnetic Waves

The mean intensity of radiation on the surface of the Sun is about $$10^8 \,W/m^2$$. The rms value of the corresponding magnetic field is closest to:

Electromagnetic Waves

A block kept on a rough inclined plane, as shown in the figure, remains at rest upto a maximum force $$2 \,N$$ down the inclined plane. The maximum external force up the inclined plane that does not move the block is $$10 \,N$$. The coefficient of static friction between the block and the plane is : [Take $$g = 10 \,m/s^2$$]

Electromagnetic Waves

The electric field in an electromagnetic wave is given by $$E=(100N/C)\sin\omega \left(t-\dfrac{x}{c}\right)$$ If the energy contained in a cylinder of cross-section $$10cm^3$$ and length $$50$$ cm along the x-axis is $$4.4\times 10^{-8} J/m^3$$, then the intensity of the wave is?

Electromagnetic Waves

The average power per unit area at distance of $$2$$ m from a small bulb, if the bulb emits $$20$$W of electromagnetic radiation uniformly in all directions, will be?

Electromagnetic Waves

A point isotropic sound source is located in the perpendicular to the plane of a ring drawn through the centre $$O$$ of the ring. The distance between the point $$O$$ and the source is $$l=1.00\ m$$ the radius of the ring is $$R=0.50\ m.$$ Find the mean energy flow across the area enclosed by the ring if at the point $$O$$ the intensity of sound is equal to $$I_{0}=30\mu\ W/m^{2}.$$ The damping of the waves is negligible.

Electromagnetic Waves

The distance from the source at which the sound is not heard.

Electromagnetic Waves

The wave intensity is defined by Eq. $$4.3i$$ $$I=\left(\Delta \right)^{2}_{m}/2\rho \nu$$

Electromagnetic Waves

The oscillation amplitude of particles of the medium; compare it with the wavelength of sound.

Electromagnetic Waves

A laser emits at 424 nm in a single pulse that lasts $$0.500 \mu s$$. The power of the pulse is 2.80MW. If we assume that the atoms contributing to the pulse underwent stimulated emission only once during the $$0.500 \mu s$$.how many atoms contributed?

Electromagnetic Waves

A light detector (your eye) has an area of $$2.00 \times 10^{-6} \mathrm{m}^{2}$$ and absorbs $$80 \%$$ of the incident light, which is at wavelength $$500 \mathrm{nm}$$. The detector faces an isotropic source, $$3.00 \mathrm{m}$$ from the source. If the detector absorbs photons at the rate of exactly $$4.000 \mathrm{s}^{-1},$$ at what power does the emitter emit light?

Contact Details