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A convex lens forms a virtual image when an object is placed at a distance of 18 cm from it. The focal length must be
- a)greater than 36 cm
- b)greater than 18 cm
- c)less than 36 cm
- d)less than 18 cm
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
A convex lens forms a virtual image when an object is placed at a dist...
A virtual image of an object is formed by a convex lens only when the object is placed between the lens and the focus. Therefore, the focal length of the lens should be greater than the distance of the object from the lens.
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A convex lens forms a virtual image when an object is placed at a dist...
Explanation:
When an object is placed at a distance of 18 cm from a convex lens, and a virtual image is formed, we can use the lens formula to determine the focal length of the lens.
The lens formula is given as:
1/f = 1/v - 1/u
where f is the focal length of the lens, v is the distance of the image from the lens, and u is the distance of the object from the lens.
In this case, the image formed is virtual, which means that v is negative. Therefore, the lens formula becomes:
1/f = -1/v - 1/u
Substituting the given values, we get:
1/f = -1/v - 1/18
Since the image is virtual, v is negative. Therefore, we can rewrite the above equation as:
1/f = 1/|v| + 1/18
Since the lens is convex, the image formed is always virtual when the object is placed between the lens and its focal point. Therefore, we know that |v| is always greater than u. This means that 1/|v| is always less than 1/u.
Therefore, we can rewrite the above equation as:
1/f < 1/u="" +="" />
Multiplying both sides by fu, we get:
u + f < f(18="" +="" />
Simplifying this equation, we get:
f > 18/2
f > 9 cm
Therefore, the focal length of the lens must be greater than 9 cm, which means that option B is the correct answer.
When an object is placed at a distance of 18 cm from a convex lens, and a virtual image is formed, we can use the lens formula to determine the focal length of the lens.
The lens formula is given as:
1/f = 1/v - 1/u
where f is the focal length of the lens, v is the distance of the image from the lens, and u is the distance of the object from the lens.
In this case, the image formed is virtual, which means that v is negative. Therefore, the lens formula becomes:
1/f = -1/v - 1/u
Substituting the given values, we get:
1/f = -1/v - 1/18
Since the image is virtual, v is negative. Therefore, we can rewrite the above equation as:
1/f = 1/|v| + 1/18
Since the lens is convex, the image formed is always virtual when the object is placed between the lens and its focal point. Therefore, we know that |v| is always greater than u. This means that 1/|v| is always less than 1/u.
Therefore, we can rewrite the above equation as:
1/f < 1/u="" +="" />
Multiplying both sides by fu, we get:
u + f < f(18="" +="" />
Simplifying this equation, we get:
f > 18/2
f > 9 cm
Therefore, the focal length of the lens must be greater than 9 cm, which means that option B is the correct answer.
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A convex lens forms a virtual image when an object is placed at a distance of 18 cm from it. The focal length must bea)greater than 36 cmb)greater than 18 cmc)less than 36 cmd)less than 18 cmCorrect answer is option 'B'. Can you explain this answer? for Class 10 2025 is part of Class 10 preparation. The Question and answers have been prepared according to the Class 10 exam syllabus. Information about A convex lens forms a virtual image when an object is placed at a distance of 18 cm from it. The focal length must bea)greater than 36 cmb)greater than 18 cmc)less than 36 cmd)less than 18 cmCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Class 10 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A convex lens forms a virtual image when an object is placed at a distance of 18 cm from it. The focal length must bea)greater than 36 cmb)greater than 18 cmc)less than 36 cmd)less than 18 cmCorrect answer is option 'B'. Can you explain this answer?.
A convex lens forms a virtual image when an object is placed at a distance of 18 cm from it. The focal length must bea)greater than 36 cmb)greater than 18 cmc)less than 36 cmd)less than 18 cmCorrect answer is option 'B'. Can you explain this answer? for Class 10 2025 is part of Class 10 preparation. The Question and answers have been prepared according to the Class 10 exam syllabus. Information about A convex lens forms a virtual image when an object is placed at a distance of 18 cm from it. The focal length must bea)greater than 36 cmb)greater than 18 cmc)less than 36 cmd)less than 18 cmCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for Class 10 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A convex lens forms a virtual image when an object is placed at a distance of 18 cm from it. The focal length must bea)greater than 36 cmb)greater than 18 cmc)less than 36 cmd)less than 18 cmCorrect answer is option 'B'. Can you explain this answer?.
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