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Anton [14]
2 years ago
14

An investigator is using a laser to illuminate a distant target. He decides that he needs a smaller beam, so he puts a pinhole d

irectly in front of the laser. He finds that this actually spreads the beam out, making matters worse.
Explain what is happening.

a. The pinhole has a size comparable with the laser wavelength, so the pinhole refracts the passing laser beam.
b. The pinhole has a size smaller than the laser wavelength, so the pinhole refracts the passing laser beam.
c. The pinhole has a size smaller than the laser wavelength, so the pinhole diffracts the passing laser beam.
d. The pinhole has a size comparable with the laser wavelength, so the pinhole diffracts the passing laser beam.
Physics
1 answer:
il63 [147K]2 years ago
7 0

Answer:

correct answer is d

The pinhole has a size comparable with the laser wavelength, so the pinhole diffracts the passing laser beam.

Explanation:

The researcher does not have a refraction problem since the medium on both sides of the pinhole is the same with the same refractive index, the problem he is having is with the diffraction of the laser beam through the pinhole, let's analyze the diffraction process that is described by the expression

          a sin θ = m λ

where a is the pinlole size,  λ the wavelength of the laser and m an integer.

The laser extends from the maximum of diffraction to the first zero (m = 1) of diffraction

         sin θ =  λ/a

when analyzing this expression we have some interesting cases

* when  λ « a. the sine approaches zero therefore we are in the case of optical geometry, in this case the laser passes through the hole without being diffracted

* when  λ ≈ a.  the sine function has values ​​between 0 and 1, for which a diffraction of the laser beam occurs, which increases the diameter of the same

* when  λ> a.  The laser does not pass through the gap since the sine cannot have values ​​greater than 1

After this analysis, we review the answers to the exercise to find that the correct answer is d

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A uniform solid disk rolls without slipping down an incline making an angle θ with the horizontal. What is its acceleration? (En
Maru [420]

Answer:

aCM = (2/3)*g*Sin θ

Explanation:

Consider a uniform solid disk having mass M,  radius R and rotational inertia I  about its center of mass, rolling without  slipping down an inclined plane.

In order to get the linear acceleration of the object’s center of mass, aCM ,

down the incline,  we analyze this as follows:

The force of gravity (W = Mg) acting straight down  is resolved into components parallel and  perpendicular to the incline.

Since the object rolls without  slipping there is a force of  friction (Ff) acting on the object,  at it’s point of contact with the  incline, in the direction up  the incline.

Newton’s 2nd Law gives then for acceleration down the incline

∑Fx' = m*aCM   ⇒    m*g*Sin θ - Ff = m*aCM

The force of friction also causes a torque around the center of mass

having lever arm R so we can also write

τ = R*Ff = I*α

Solving for the friction,    Ff = I*α / R

This is used in the expression  derived from the 2nd Law:

m*g*Sin θ - Ff = m*g*Sin θ - (I*α / R) = m*aCM

The objects angular acceleration is related to the linear acceleration  of the edge that contacts the incline by

a = R*α

Since the object rolls without  slipping this has the same  magnitude as aCM so we have  that

α = aCM / R

Using this in

m*g*Sin θ - (I*α / R) = m*g*Sin θ - (I*(aCM / R) / R) = m*aCM

⇒  aCM = (m*g*Sin θ*R²) / (I + m*R²)

if I = (1/2)*m*R²   (for a uniform solid disk)

we get

aCM = (2/3)*g*Sin θ

6 0
3 years ago
What is the equation for force
Basile [38]
The equation is F=ma :)
3 0
3 years ago
Read 2 more answers
when do you use cos and sin in situations like these? is horizontal always cos and vertical always sin?
Andreas93 [3]

Answer:

yes

Explanation:

this is simple

the horizontal line is adjacent

the vertical line is opposite

recall that cos x=adj/hyp

adj=hyp(cos x)

while opp=hyp(sin x)

8 0
3 years ago
Which type of macromolecules a cell brake down food?
kobusy [5.1K]

Answer:

Hope this helps you find the answer

Explanation:

The proteins, lipids, and polysaccharides that make up most of the food we eat must be broken down into smaller molecules before our cells can use them—either as a source of energy or as building blocks for other molecules.

8 0
3 years ago
The drawing shows an adiabatically isolated cylinder that is divided initially into two identical parts by an adiabatic partitio
Sveta_85 [38]

Answer:

temperature on left side is 1.48 times the temperature on right

Explanation:

GIVEN DATA:

\gamma = 5/3

T1 = 525 K

T2 = 275 K

We know that

P_1 = \frac{nRT_1}{v}

P_2 = \frac{nrT_2}{v}

n and v remain same at both side. so we have

\frac{P_1}{P_2} = \frac{T_1}{T_2} = \frac{525}{275} = \frac{21}{11}

P_1 = \frac{21}{11} P_2 ..............1

let final pressure is P and temp  T_1 {f} and T_2 {f}

P_1^{1-\gamma} T_1^{\gamma} = P^{1 - \gamma}T_1 {f}^{\gamma}

P_1^{-2/3} T_1^{5/3} = P^{-2/3} T_1 {f}^{5/3} ..................2

similarly

P_2^{-2/3} T_2^{5/3} = P^{-2/3} T_2 {f}^{5/3} .............3

divide 2 equation by 3rd equation

\frac{21}{11}^{-2/3} \frac{21}{11}^{5/3} = [\frac{T_1 {f}}{T_2 {f}}]^{5/3}

T_1 {f} = 1.48 T_2 {f}

thus, temperature on left side is 1.48 times the temperature on right

6 0
3 years ago
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