Image in Thin Lens Using Formula

Q. A thin lens of focal length $f$ and its aperture diameter $d$, forms a real image of intensity $I$. Now the central part of the aperture of diameter $\left(\frac{d}{2}\right)$ is blocked by an opaque paper. The focal length and image intensity would change to

1. $\frac{f}{2},\frac{I}{2}$
2. $f,\frac{I}{4}$
3. $\frac{3f}{4},\frac{I}{2}$
4. $f,\frac{3I}{4}$

Q. A concave lens forms the image of an object such that the distance between the object and image is 10 cm and the magnification proceed is $\frac{1}{4}$. The focal length of the lens will be

1. 8.6 cm
2. 6.2 cm
3. 10 cm
4. 4.4 cm

Q. An object is placed at a distance of $\frac{f}{2}$ from a convex lens. The image will be

1. At one of the foci, virtual and double its size
2. At $\frac{3f}{2}$, real and inverted
3. At 2f, virtual and erect
4. None of these

Q. A point object $O$ is placed at a distance of $0.3m$ from a convex lens $($focal length $0.2m)$ cut into two halves each of which is displaced by $0.0005m$ as shown in the figure.

What will be the location of the image?

1. $30cm,$ right of lens
2. $60cm,$ right of lens
3. $70cm,$ left of lens
4. $40cm,$ left of lens