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3 years ago

What is the difference between protraction and retraction?

Physics

1 answer:

Nina [5.8K]3 years ago

6 0

Answer:

Protraction and retraction are opposite of each other.

Explanation: For example, here are difference between the two.

1. Protraction occurs when the lower has is pushed forward to stick to the chin, Retraction, being the opposite pulls the lower jaw backward.

2. Scapular retraction, this help to move the shoulder blade(scapula) towards the spine, also Protraction being the opposite help to move the shoulder blade away from the spine.

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A given individual is unable to see objects clearly when he is beyond 60 cm. What power lens should be used to correct this prob

Sveta_85 [38]

Answer:

correct option is E

power lens is - 1.667 D

Explanation:

Given data

infinity = 60 cm

to find out

power lens

solution

we know here infinity v = -60 cm because object at infinity

and we take u = - infinity

so we know that

1/f = 1/v - 1/u

1/f = 1 / -60 - 1 / -infinity

1/f = - 1/60

f = - 60 cm = 0.60 m

and we know power of lens = 1/f

so here

power = 1 / -0.60

power = - 1.667 D

so correct option is E

power lens is - 1.667 D

6 0

4 years ago

Solar cells convert what type of energy into electrical energy?

zysi [14]

I think the correct answer from the choices listed above is option D. Solar cells convert electromagnetic energy into electrical energy. This is because the photons from the rays of light are electromagnetic waves or particles. Hope this answers the question.

6 0

4 years ago

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In 1929, American astronomer Edwin Hubble discovered that distant galaxies were moving away from us. He found that light from di

Novay_Z [31]

Answer:

it is the Hubble law

Explanation:

Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from the Earth at speeds proportional to their distance. In other words, the farther they are the faster they are moving away from Earth.

7 0

3 years ago

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On the kelvin scale what is the freezing point of water

Alla [95]

Freezing point of the water is known as 273 K

Hope this helps!

8 0

3 years ago

A physicist drives through a stop light. When he is pulled over, he tells the police officer that the Doppler shift made the red

makkiz [27]

Answer:

Explanation:

$\lambda$ = Observed wavelength = 550 nm

$\lambda'$ = Actual wavelength = 635 nm

c = Speed of light = $3\times 10^8\ \text{m/s}$

v = Velocity of the physicist

Doppler shift is given by

$f=\sqrt{\dfrac{c+v}{c-v}}f'\\\Rightarrow \dfrac{c}{\lambda}=\sqrt{\dfrac{c+v}{c-v}}\dfrac{c}{\lambda'}\\\Rightarrow \dfrac{\lambda'^2}{\lambda^2}=\dfrac{c+v}{c-v}\\\Rightarrow \dfrac{\lambda'^2}{\lambda^2}=\dfrac{1+\dfrac{v}{c}}{1-\dfrac{v}{c}}\\\Rightarrow \dfrac{\lambda'^2}{\lambda^2}(1-\dfrac{v}{c})=1+\dfrac{v}{c}\\\Rightarrow \dfrac{\lambda'^2}{\lambda^2}(1-\dfrac{v}{c})=1+\dfrac{v}{c}\\\Rightarrow \dfrac{\lambda'^2}{\lambda^2}-1=\dfrac{v}{c}(1+\dfrac{\lambda'^2}{\lambda^2})\\\Rightarrow v=\dfrac{c(\dfrac{\lambda'^2}{\lambda^2}-1)}{1+\dfrac{\lambda'^2}{\lambda^2}}$

$\Rightarrow v=\dfrac{3\times 10^8\times (\dfrac{635^2}{550^2}-1)}{1+\dfrac{635^2}{550^2}}\\\Rightarrow v=42817669.77\ \text{m/s}$

The physicist was traveling at a velocity of $42817669.77\ \text{m/s}$ .

4 0

3 years ago