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sertanlavr [38]
3 years ago
5

An LED with total power P tot = 960 mW emits UV light of wavelength 360 nm. Assuming the LED is 55% efficient and acts as an iso

tropic point source (i.e., emits light uniformly in all directions), what is the amplitude of the electric field, E 0 , at a distance of 2.5 cm from the LED?
Physics
1 answer:
Anit [1.1K]3 years ago
4 0

Answer:

E_0=225.09N/C

Explanation:

We are given that

Power,Ptot=960mW=960\times 10^{-3}W

1mW=10^{-3} W

Wavelength,\lambda=360 nm=360\times 10^{-9} m

1nm=10^{-9} m

Distance,r=2.5 cm=2.5\times 10^{-2} m

1m=100 cm

Efficiency=55%

Power radiation emitted=\frac{55}{100}\times 960\times 10^{-3}=0.528W

Intensity,I=\frac{P}{4\pi r^2}

I=\frac{0.528}{4\pi(2.5\times 10^{-2})^2}=67.26W/m^2

Intensity,I=\frac{1}{2}c\epsilon_0E^2_0

E^2_0=\frac{2I}{c\epsilon_0}

Where \epsilon_0=8.85\times 10^{-12}

c=3\times 10^8 m/s

E_0=\sqrt{\frac{2I}{c\epsilon_0}}

E_0=\sqrt{\frac{2\times 67.26}{3\times 10^8\times 8.85\times 10^{-12}}}

E_0=225.09N/C

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What are the change in internal energy if 250 j of hear is added to a system of 80 j of work is done by the system
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Answer:

Explanation:

dU= dq+w

dU is change in internal energy of the system

dq is the amount heat added or released by the system which be positive or negative respectivelý

And w is the amount of work done by the system or on the system which will be positive or negative respectively.

Hence,

dU= 250+80= 330 J

The change will be positive

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A 0.5 kg yellow bouncy ball rolls to the right at a speed of 8 m/s while a 0.25 kg blue bouncy ball rolls
inessss [21]

Explanation:

Let yellow ball be m1 = 0.5kg with u1 = 8 m/s and blue ball be m2 = 0.25 kg with u2 = - 4 m /s respectively.

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<u>Using conservation of Linear Momentum</u> :

m1u1 + m2u2 = m1v1 + m2v2

0.5* 8 + 0.25 * - 4 = 0.5 * v1 + 0.25 * 12

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3 0
2 years ago
Linear distance: parsec:: angular diameter: _______
mafiozo [28]

Answer:

Angular diameter : degrees or radians

Explanation:

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What is the critical angle for light going from crown glass to air?
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Answer:

The critical angle for a diamond in air is 24 degrees, while the critical angle for glass is 41 degrees.

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3 years ago
PHYSICS PLEASE HELP 80 PTS!!!!!!
VladimirAG [237]

1.  B) 32 m/s

The speed of the baseball is given by

v=\frac{d}{t}

where

d = 48 m is the distance travelled

t = 1.5 s is the time taken

Substituting,

v=\frac{48}{1.5}=32 m/s

2. C) 12 m/s

The average velocity is given by

v=\frac{d}{t}

where

d = 60 - 0 = 60 m is the displacement

t = 5 s is the time interval

Substituting,

v=\frac{60}{5}=12 m/s

3. Missing diagram

4. D) velocity

In fact, velocity is defined as the ratio between the displacement (\Delta s) and the time interval (\Delta t) needed to achieve that change in position:

v=\frac{\Delta s}{\Delta t}

Similarly, acceleration is defined as the ratio between the change in velocity (\Delta v) and the time interval (\Delta t):

a=\frac{\Delta v}{\Delta t}

Comparing the two equations, we see that displacement is to velocity as velocity is to acceleration.

5. C) 5/1 cm/year

We know that the ridge moves 25 cm in 5 years, so we have:

- Displacement (d): d = 25 cm

- Time interval (t): t = 5 y

Using the equation for the velocity:

v=\frac{d}{t}=\frac{25 cm}{5 y}=5 cm/y

6.  D

The missing graph is attached. Each graph represents a distance (on the y-axis, measured in metres) versus a time (on the x-axis, measured in seconds). Therefore, the speed in each graph can be simply calculated from the slope of the curve, since speed is the ratio between distance and time:

v=\frac{\Delta y}{\Delta x}

For each graph:

A. \frac{\Delta y}{\Delta x}=\frac{8.6-2}{10}\sim 0.66

B. \frac{\Delta y}{\Delta x}=\frac{5.7-0}{10}\sim 0.57

C. \frac{\Delta y}{\Delta x}=\frac{9.6-3}{10}\sim 0.66

D. \frac{\Delta y}{\Delta x}=\frac{7.5-0}{5}\sim 1.5

So we can say that the correct graph must be graph D, the closest to 1.57.

7. B) The car has come to a stop and has zero velocity

The missing graph is attached.

The graph shows the position of the car versus time. From the graph, we can see that in segment B, the position of the car does not change: this means that its velocity is zero, since the velocity is defined as the ratio between the change in position (displacement) and the time interval:

v=\frac{\Delta s}{\Delta t}

And since the displacement is zero, the velocity is also zero.

8.  C) from 4.5 to 5.0 seconds

Missing graph is attached.

The graph represents the distance covered versus the time taken: therefore, the speed of the ball can be evaluated from the slope of the curve.

The only region in which the slope of the curve is zero is between 4.5 seconds and 5.0 seconds: therefore, this is the region where the soccer ball is not moving.

9. D) diagonal line with varying slope, from 3 to 4.

The table of data is:

Time (s)  0 1 2 3 4

Distance (m) 0 3 6 12 16

We want to know how the distance/time graph would like like. We have:

- At t = 1, the distance is d=3, so the slope is \frac{d}{t}=\frac{3}{1}=3

- Similarly, at t = 2:  \frac{d}{t}=\frac{6}{2}=3

- Instead, at t =3, the slope is \frac{d}{t}=\frac{12}{3}=4

- Similarly, at t=4,\frac{d}{t}=\frac{16}{4}=4

So the correct answer is D.

10. D) To move in a circle requires an acceleration and therefore a net force. This force is supplied by the slingshot.

For an object in circular motion, the velocity constantly changes (because the direction changes): this means that an acceleration is required (towards the centre of the circle), and therefore a force must be exerted (also towards the centre of the circle) to keep the object in the circular path.

As soon as this force is removed, the object is "free" to leave the circular trajectory and continue its motion following a straight path at constant velocity, according to Newton's first law.

11. B) The acceleration will become 1/4 as much.

Re-arranging Newton's second law formula,

F=ma \rightarrow a = \frac{F}{m} (1)

The force exerted on the satellite is actually the force of gravity:

F=\frac{Gm M}{d^2} (2)

Substituting (2) into (1),

a=\frac{F}{m}=\frac{GM}{d^2}

We see that there is no dependance on the mass of the satellite (m), but only on the distance. Since in this problem the distance is doubled (d'=2d), the new acceleration will be:

a'=\frac{GM}{(2d)^2}=\frac{1}{4}(\frac{GM}{d^2})=\frac{a}{4}

12. C) divide: distance : velocity

Velocity is distance divided by time:

v=\frac{d}{t}

Multiplying by t on both sides,

v\cdot t = \frac{d}{t} \cdot t \rightarrow vt = d

and dividing by v on both sides,

\frac{vt}{v}=\frac{d}{v} \rightarrow t = \frac{d}{v}

13. A) -8 km/h

Let's call:

v_k = +5 km/h the velocity of the kite

v_p = -3 km/h your velocity (opposite direction)

In your frame of reference, the velocity of the kite will be:

v'_k = v_p - v_k = -3 -(+5) = -8 km/h

3 0
3 years ago
Read 2 more answers
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