PHYSICS COLLEGE

Where is the near point of an normal eye when accidentally wear a contact lens with a power of +2.0 diopters?

Answers

Answer 1

Answer:

Answer:

The near point of an eye with power of +2 dopters, u' = - 50 cm

Given:

Power of a contact lens, P = +2.0 diopters

Solution:

To calculate the near point, we need to find the focal length of the lens which is given by:

Power, P = $(1)/(f)$

where

f = focal length

Thus

f = $(1)/(P)$

f = $(1)/(2)$ = + 0.5 m

The near point of the eye is the point distant such that the image formed at this point can be seen clearly by the eye.

Now, by using lens maker formula:

$(1)/(f) = (1)/(u) + (1)/(u')$

where

u = object distance = 25 cm = 0.25 m = near point of a normal eye

u' = image distance

Now,

$(1)/(u') = (1)/(f) - (1)/(u)$

$(1)/(u') = (1)/(0.5) - (1)/(0.25)$

$(1)/(u') = (1)/(f) - (1)/(u)$

Solving the above eqn, we get:

u' = - 0.5 m = - 50 cm

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Interactive Solution 9.1 presents a model for solving this problem. The wheel of a car has a radius of 0.380 m. The engine of the car applies a torque of 456 N·m to this wheel, which does not slip against the road surface. Since the wheel does not slip, the road must be applying a force of static friction to the wheel that produces a countertorque. Moreover, the car has a constant velocity, so this countertorque balances the applied torque. What is the magnitude of the static frictional force?

Answers

Answer:

The magnitude of the static frictional force is 1200 N

Explanation:

given information :

radius, r = 0.380 m

applied-torque, τ1 = 456 N

The car has a constant velocity, thus the acceleration is zero

α = 0

Στ = I α

τ1 - τ2 = I α

τ2 = counter-torque

τ1 - τ2 = 0

τ1 = τ2

r x $F_(s)$ = τ1

$F_(s)$ = the static frictional force (N)

$F_(s)$ = τ1 /r

= 456 N/0.380 m

= 1200 N

An early model of the atom, proposed by Rutherford after his discovery of the atomic nucleus, had a positive point charge +Ze (the nucleus) at the center of a sphere of radius R with uniformly distributed negative charge −Ze. Z is the atomic number, the number of protons in the nucleus and the number of electrons in the negative sphere. Show that the electric field inside this atom is : Ein=Ze4πϵ0(1r^2−rR^3). b. What is the electric field at the surface of the atom? Is this the expected value? Explain.c. A uranium atom has Z = 92 and R = 0.10 nm. What is the electric field at r = R/2?

Answers

Answer:

Part a)

$E = (Ze)/(4\pi\epsilon_0)((1)/(r^2) - (r)/(R^3))$

Part b)

$E = 0$

Yes it is the expected value of electric field at the surface of an atom

Part c)

$E = 4.64 * 10^(13) N/C$

Explanation:

Since negative charge of electrons in uniformly distributed in the atom while positive charge is concentrated at the nucleus

So the electric field due to positive charge of the nucleus is given as

$E = (kq)/(r^2)$

$E_1 = (Ze)/(4\pi \epsilon_0 r^2)$

now charge due to electrons inside a radius "r" is given as

$q = (-Ze r^3)/(R^3)$

now we will have electric field given as

$E_2 = ((-Zer^3)/(R^3))}{4\pi\epsilon_0 r^2}$

now net electric field is given as

$E = E_1 + E_2$

$E = (Ze)/(4\pi \epsilon_0 r^2) - (Zer)/(4\pi \epsilon_0 R^3)$

$E = (Ze)/(4\pi\epsilon_0)((1)/(r^2) - (r)/(R^3))$

Part b)

At the surface of an atom

$r = R$

$E = 0$

Yes it is the expected value of electric field at the surface of an atom

Part c)

If Z = 92

R = 0.10 nm

$r = (R)/(2)$

so we will have

$E = 92(1.6 * 10^(-19)) * (9 * 10^9)((4)/(R^2) - (1)/(2R^2))$

$E = (4.64 * 10^(-7))/((0.10 * 10^(-9))^2)$

$E = 4.64 * 10^(13) N/C$

Air trapped in the cooling system could create undesirable areas of combustion heat buildup in the engine called _____.

Answers

Answer:

Air pockets.

Explanation:

Air pockets in the cooling system are bubbles of air trapped within the lines (hoses and pipes) of the cooling system. This air bubbles enter the cooling system usually during the process of filling the radiator coolant fluid (usually water), or replacing the water pump or the radiator hose during repairs or servicing of the cooling system. The trapped air prevent pressure movement that is needed by the coolant to move the heat generated from the engine cylinder, resulting in heat build up. The solution is to "bleed" the engine through the radiator lid or some air release valves.

Most elements in nature exist as mixture of two or more isotopes
t or f

Answers

Answer:

Atomic mass is a value that depends on the distribution of an element's isotopes in nature and the masses of those isotopes. Circle the letter of each sentence that is true about a carbon-12 atom. ... Most elements exist as a mixture of two or more isotopes.

So the answer is true.

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The animal that is hunted and consumed is considered the

Answers

Predator? like they hunt their prey

Answer:

prey

Explanation:

The height of the upper falls at Yellowstone Falls is 33 m. When the water reaches the bottom of the falls, its speed is 26 m/s. Neglecting air resistance, what is the speed of the water at the top of the falls?