Total Power of Lenses in Contact:
When lenses are kept in contact, the effective power \( P_{eq} \) is the sum of the individual powers of each lens:
\[ P_{eq} = \sum P_i \]
Given that there are 5 identical lenses and the total power is 25 D, we have:
\[ 5P = 25 \implies P = \frac{25}{5} = 5 \, \text{D} \]
where \( P \) is the power of each individual lens.
Calculate the Focal Length:
The focal length \( f \) of a lens is related to its power \( P \) by:
\[ P = \frac{1}{f} \]
where \( f \) is in meters if \( P \) is in diopters (D).
Therefore:
\[ f = \frac{1}{P} = \frac{1}{5} = 0.2 \, \text{m} = 20 \, \text{cm} \]
Conclusion:
The focal length of each convex lens is 20 cm.
Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R):
Assertion (A): An electron in a certain region of uniform magnetic field is moving with constant velocity in a straight line path.
Reason (R): The magnetic field in that region is along the direction of velocity of the electron.
In the light of the above statements, choose the correct answer from the options given below: