Question

If the radius of base of a cylinder is doubled and the height remains unchanged, its curved surface area becomes:

• A. double
• B. three times
• C. half
• D. no change

Answer 1

The correct option is A double

Let the height of the cylinder be $h$ and radius of its base be $r$.

Therefore, curved surface area of cylinder $2\pi rh$

Now, the radius is doubled. So, the new radius $r^{\prime }$ is $=2r$

New curved surface area $=2\pi r^{\prime }h$

$=2\pi \times 2r\times h=2\times 2\pi rh=2\text{(Curved surface area of old cylinder)}$

Hence, curved surface area of new cylinder is doubled after doubling the radius.