Answer: f = -12 cm
Explanation: <u>Combined</u> <u>lenses</u> is an array of simple lenses with a common axis. The combination is useful for correction of optical aberrations which cannot be corrected by simple lenses.
When two lenses are in contact and are thin, focal lengths are related as:

If there is a distance between the lenses, the focal length will be:

Since the lenses in the question above are thin and in contact, the focal length of one of them will be:




-12
The focal length of the other lens is -12 cm, with the negative sign meaning it's a converging lens.
There are no rules that describe how positive energy behaves
in the presence of negative energy, because there is no such
thing as negative energy.
(Wellll ... in pop Psychology, perhaps, but not in any real science.)
Answer:
number of Protons=16
number of Neutrons=16
number of electrons=32
Explanation:
Tip:-
<em><u>Always the number of protons = the number of neutrons.</u></em>
<em><u>Add them and you will get the number of electrons.</u></em>
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The work done by the elephant to lift one log is the force multiplied by the height at which the log has been lifted:

And so, the total work done to lift the 7 logs is 7 times the work done to lift each log: