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klasskru [66]
2 years ago
8

An individual white LED (light-emitting diode) has an efficiency of 20% and uses 1.0 W of electric power. a. How many LEDs must

be combined into one light source to give a total of 1.6 W of visible-light output (comparable to the light output of a 40 W incandescent bulb)? b. What total power is necessary to run this LED light source?
Physics
1 answer:
Neporo4naja [7]2 years ago
7 0

Answer:

8, 8 W

Explanation:

The useful power of 1 Light Emitting Diode is

0.2\times 1=0.2\ W

Total power required is 1.6 W

Number of Light Emitting Diodes would be

n=\dfrac{1.6}{0.2}\\\Rightarrow n=8

The number of Light Emitting Diodes is 8.

Power would be

P=8\times 1=8\ W

The power that is required to run the Light Emitting Diodes is 8 W

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Determine the sign (+ or −) of the torque about the elbow caused by the biceps, τbiceps, the sign of the weight of the forearm,
Alex Ar [27]
Ans: 
1.  τbiceps = +(Positive)
2.  τforearm = -(Negative)
3.  τball = -(Negative)

Explanation:

The figure is attached down below.

1. T<span>orque about the elbow caused by the biceps, τbiceps:
Since Torque = r x F (where r and F are the vectors)
</span>Where r is the vector from elbow to the biceps.
<span>
We can see in the figure that F(biceps) is in upward direction, and by applying the right hand rule from r to F, we get the counterclockwise direction. The torque in counterclockwise direction is positive(+). Therefore, the sign would be +.

2. </span>Torque about the the weight of the forearm, τforearm:
Since Torque = r x F (where r and F are the vectors)
Where r is the vector from elbow to the forearm.

Also weight is the special kind of Force caused by the gravity.

We can see in the figure that W(forearm) is in downward direction, and by applying the right hand rule from r to F, we get the clockwise direction. The torque in clockwise direction is negative(-). Therefore, the sign would be -.

3. Torque about the the weight of the ball, τball:
Since Torque = r x F (where r and F are the vectors)
Where r is the vector from elbow to the ball.

Also weight is the special kind of Force caused by the gravity.

We can see in the figure that W(ball) is in downward direction, and by applying the right hand rule from r to F, we get the clockwise direction. The torque in clockwise direction is negative(-). Therefore, the sign would be -.

8 0
2 years ago
Torque, a car manufacturer, aims to make its slogan "Burn Rubber" known to every individual in a way that they immediately assoc
mylen [45]

Answer:

A customer is about to buy a limited edition sports car from Torque. It is most likely that the customer will have  d. limited problem solving, in which consumers decision rules to purchase are simple, and are not motivated to search for information about other optons, deciding to buy the car.

Explanation:

a. advertising clutter is the big amount of ad-messages that the consumer is exposed to everyday.

b. high involvement  product or purchases features many variables to be considered by the customer before getting to a decision.

c. cognitive dissonance  or conflicting attitudes causing mental discomfort.

7 0
2 years ago
The escape velocity is defined to be the minimum speed with which an object of mass m must move to escape from the gravitational
s344n2d4d5 [400]

Answer:

v = √2G M_{earth} / R

Explanation:

For this problem we use energy conservation, the energy initiated is potential and kinetic and the final energy is only potential (infinite r)

        Eo = K + U = ½ m1 v² - G m1 m2 / r1

        Ef = - G m1 m2 / r2

When the body is at a distance R> Re, for the furthest point (r2) let's call it Rinf

       Eo = Ef

       ½ m1v² - G m1 M_{earth} / R = - G m1 M_{earth} / R

      v² = 2G M_{earth} (1 / R - 1 / Rinf)

If we do Rinf = infinity     1 / Rinf = 0

       v = √2G M_{earth} / R

      Ef = = - G m1 m2 / R

The mechanical energy is conserved  

 

      Em = -G m1  M_{earth} / R

      Em = - G m1  M_{earth} / R

     R = int        ⇒  Em = 0

6 0
1 year ago
Calculate the density of mercury if 500 cm3
notka56 [123]

Answer:

The density of the mercury is 13.2 g/cm³

Explanation:

Density is a measurement that compares the amount of matter an object

has to its volume

Density is equal to mass divided by volume

We need to find the density of mercury if 500 cm³ has a mass of

6.60 kg in g/cm

We must to change The kilogram to grams

The mass of mercury is 6.60 kilograms

1 kilogram = 1000 grams

6.60 kilograms = 6.60 × 1000 = 6600 grams

Density = mass ÷ volume

The volume of the mercury is 500 cm³

The density = 6600 ÷ 500

The density = 13.2 g/cm³

<em>The density of the mercury is 13.2 g/cm³ </em>

5 0
2 years ago
A spherical capacitor is formed from two concentric sphericalconducting shells separated by vacuum. The inner sphere has radius1
Tema [17]

Answer:

Δ V = 38.74 V, W= 6.39 × 10 ⁻⁸ J

Explanation:

Given: Let inner Sphere Radius r1 = 10.0 cm = 0.1 m

separation d = 1.50 cm = 0.015 m

so the radius of outer sphere will be 0.1 + 0.015 = 0.115 m =r2

charge Q = 3.30 nC= 3.30 × 10 ⁻⁹ C

K= 9.0 x 10⁹ N • m² / C²

To Find: Δ V= ? and W=?

Solution:

1) we know that   Δ V = K Q / (1/r1 - 1/r2)

Δ V = 9.0 x 10⁹ N • m² / C² × 3.30 × 10 ⁻⁹ C / (1/0.1 - 1/0.115)

Δ V = 38.74 V

2) W = VQ/2    

W=   1980 V  × 3.30 × 10 ⁻⁹ C /2

W= 6.39 × 10 ⁻⁸ J

7 0
2 years ago
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