### All MCAT Physical Resources

## Example Questions

### Example Question #1 : Focal Length

The focal point for a mirror is 56cm behind the mirror. Is the mirror concave or convex, and what is its radius of curvature?

**Possible Answers:**

Concave with radius of curvature of 28cm

Convex with radius of curvature of 28cm

Concave with radius of curvature of 112cm

Convex with radius of curvature of 112cm

**Correct answer:**

Convex with radius of curvature of 112cm

Since the focal point falls behind the mirror it must be **convex**. The radius of curvature can be found using the focal length equation.

### Example Question #2 : Focal Length

A concave mirror has a radius of curvature of 0.85m. Where is the mirror's focal point?

**Possible Answers:**

The focal point cannot be found from the given information

**Correct answer:**

Since the mirror is concave, the focal point will be in **front** of the mirror. The focal length is equal to one half of the radius of curvature.

R_{c} is the radius of curvature. Plugging in 0.85m for R_{c} allows us to solve for the focal length.

0.43m is equal to 43cm.

### Example Question #3 : Focal Length

A lens has a focal length of . What is the strength and type of lens?

**Possible Answers:**

, converging lens

, diverging lens

, diverging lens

, converging lens

**Correct answer:**

, diverging lens

Since the focal length is negative, the lens is diverging.

The diopter of a lens is found through the following formula:

Since the focal length of the lens is :

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