A lens of focal length 15cm forms an erect image which is three times the size of the object. The distance between the object and the image is ___.

Iphie101

3 years ago

In lens, when a virtual image is formed, it is on the same side as the object. Therefore, the distance between an object and it's virtual image should be gotten by subtraction not addition. So the answer ought to be 30-10 =20cm

bodmas2020

2 years ago

please hoo where did the in the video see mirror in the question?
and we were asked the difference between their distance so how come you are now adding up theur destance rather than subtracting it?
it clear that the answer is B 20cm please make amendment jare.

Brightonexcellent

1 year ago

To solve this, we use the lens formula and magnification formula:

Step 1: Use the magnification formula

Since the image is erect and three times the size of the object, magnification (positive because the image is erect, which indicates a virtual image and hence a convex lens used in this case).

M = v/u
3 = v/u. v = 3u

Step 2: Use the lens formula

1/f = 1/v - 1/u

Given focal length (positive for a convex lens), and from above , substitute into the formula:

1/15= 1/3u - 1/u

Find a common denominator:

1/15 =( 1 - 3)/3u= -2/3u

Now solve:

1/15 = -2/3u
3u = -30
u = -10 cm

So object distance , and image distance:

v = 3u = 3(-10) = -30 cm

Step 3: Find distance between object and image

Distance= |v - u| = |-30 - (-10)| = |-30 + 10| = |-20| = 20 cm

Final Answer:

B. 20 cm

Dave333

4 years ago

I guess convex lens form erect image,That means,The focal length takes negative

Dave333

4 years ago

But, There is no concave or convex lens here🤷

Brodan1

2 years ago

Aah what is this? i dont really understand.
Can a convex mirror or lens form a magnified Image?

Definitely not. Now why did you now represent with a negative value?

DevChris

4 weeks ago

ai explainer says answer is option b though