A professor reads a greeting card received on his 50th birthday with + 2.5D glasses keeping the card 25 cm away.
A professor reads a greeting card received on his 50th birthday with + 2.5D glasses keeping the card 25 cm away. Ten years later, he reads his farewell letter with the same glasses but he has 'to keep the letter 50 cm away. What power of lens should he now use ?
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