Answer:
f = 19,877 cm and P = 5D
Explanation:
This is a lens focal length exercise, which must be solved with the optical constructor equation
1 / f = 1 / p + 1 / q
where f is the focal length, p is the distance to the object and q is the distance to the image.
In this case the object is placed p = 25 cm from the eye, to be able to see it clearly the image must be at q = 97 cm from the eye
let's calculate
1 / f = 1/97 + 1/25
1 / f = 0.05
f = 19,877 cm
the power of a lens is defined by the inverse of the focal length in meters
P = 1 / f
P = 1 / 19,877 10-2
P = 5D
Answer:
Explanation:
Power is related to energy by the following relationship:
where
P is the power used
E is the energy used
t is the time elapsed
In this problem, we know that
- the power of the fan is P = 120 W
- the fan has been running for one hour, which corresponds to a time of
So we can re-arrange the previous equation to find E, the energy (in the form of thermal energy) released by the fan:
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