# Magnifying Power and Focal Length of a Lens

Magnifying power Is how much larger a given lens can make an image appear. This is a direct relationship between the focal length of the lens and the Least distance of distinct vision, or LDDV. The LDDV is the closest your eyes can comfortably look at an object.

### Objective

Which magnifying glass is the most powerful?

### Materials

• Magnifying glasses of different sizes or powers
• Wall
• Flashlight
• Metre stick
• Stuff to magnify!

### Procedure

1. For each magnifying glass, stand close to a wall and shine the flashlight through each magnifying glass onto the wall.
2. Move the flashlight closer to or farther away from the wall until the light refracts to a single point.
3. Measure the distance from the lens to the wall to get a reading (in centimeters) to find the focal length. It can be handy to have a friend help you here.
4. Create a table to manage your data.
5. Now, choose a small object. Bring the object as close to your eyes as you can before it becomes blurry and out of focus.
6. Measure and record this distance. This is the Least Distance of Distinct Vision, or LDDV.
7. Calculate the magnifying power of each magnifying lens. Use the following formula.

Where MpIs Magnifying power, LDDVIs the least distance of distinct vision you found in step 7, and LFIs the focal length of the lens.

1. Test it out! Do your observations match up with each calculated magnifying power? Take a look at how the same object looks under different magnifying glasses to compare.

### Results

The distance of distinct vision is usually somewhere around 10 cm for a person with perfect vision. Magnifying lenses with shorter focal lengths will have greater magnifying power.

### Why?

Magnifying power is InverselyRelated to the focal length of a lens: the bigger the focal length, the lower the magnifying power. The LDDV is a ConstantNumber, as it usually tends to be the same for people with good vision. Focal length and LDDV have to be measured in the same units for the calculations to work out—they’re usually measured in meters (or centimeters).

Another feature of lenses is called Lens power, very similar to magnifying power, and is expressed in the following relationship:

The units of focal length LfAre meters. Lens power is therefore measured in 1/m, also called Diopters.

Disclaimer and Safety Precautions

Education.com provides the Science Fair Project Ideas for informational purposes only. Education.com does not make any guarantee or representation regarding the Science Fair Project Ideas and is not responsible or liable for any loss or damage, directly or indirectly, caused by your use of such information. By accessing the Science Fair Project Ideas, you waive and renounce any claims against Education.com that arise thereof. In addition, your access to Education.com's website and Science Fair Project Ideas is covered by Education.com's Privacy Policy and site Terms of Use, which include limitations on Education.com's liability.

Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state's handbook of Science Safety.

Create new collection

0

### New Collection>

0Items

What could we do to improve Education.com?