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Answer:
The focal length of the lens should be -51.5 cm (a concave lens).
Explanation:
The purpose of the lens is to make objects at 48.5 cm appear at the healthy near point. The healthy near point is 25.0 cm.
We use the lens formula
where <em>f</em> = focal length, <em>u</em> = object distance and <em>v</em> = image distance.
In this case, <em>u</em> = 48.5 cm and <em>v</em> = -25.0 cm.
<em>v</em> is negative because the image is virtual an not real. (Here, we are using the real-is-positive sign convention)
The negative sign indicates the lens is concave.
First let's convert the time in seconds:
The current is defined as the quantity of charge flowing through a certain section of a circuit per unit of time:
Using I=10 A, and
, we can find the amount of charge flown through the hair dryer in this time:
The charge of a single electron is
, so the number of electrons flown through the hair dryer is the total charge divided by the charge of a single electron:
The current is defined as the quantity of charge flowing through a certain section of a circuit per unit of time:
Using I=10 A, and
The charge of a single electron is