These questions ask you to connect each microscope part with its job, choose a safe focusing control, or calculate magnification and size. You can solve them by identifying the required action before naming a part or choosing an equation.
Match the job, then use the size triangle
For a part question, turn the description into a verb. Viewing points to the eyepiece, magnifying beside the slide points to an objective, selecting among objectives points to the revolving nosepiece or turret, and supporting the slide points to the stage. Supplying light is the illuminator's job; changing how much transmitted light reaches the specimen is the diaphragm's job. Large initial movements at low power use coarse focus, while small sharpening movements use fine focus. For example, if an image is visible but slightly fuzzy, the required verb is sharpen, not select.
| Signal in the task | Method |
|---|---|
| Two lens powers are given | Multiply eyepiece power by objective power. Successive enlargement is a product, not a sum. |
| Image size and actual size are given | Convert to matching units, then divide image size by actual size. |
| Magnification and image size are given | Rearrange the same relationship: actual size equals image size divided by magnification. |
| Millimetres must become micrometres | Multiply by one thousand. Going from micrometres to millimetres uses division by one thousand. |
Keep units beside every value until they match. As a fresh example, an image measuring 6 millimetres of a specimen that is 0.03 millimetres long has a magnification found by 6 divided by 0.03. If the required quantity were actual size instead, cover actual size in the relationship and divide image size by magnification.
Avoid these tempting routes
| Tempting route | How to reject it |
|---|---|
| Choose the objective because both lenses magnify | Ask where the observer looks. The objective is beside the slide; the eyepiece is at the viewing end. |
| Use a focus control to change lens power | Focusing changes sharpness or position, whereas rotating the nosepiece selects another objective. |
| Choose a focusing, lens-selection, or lighting part to support the slide | Those parts sharpen the image, select an objective, or supply light. The platform directly beneath the slide provides its support. |
| Choose a focusing or slide-holding part when light must be supplied | The illuminator supplies the light. Focus controls sharpen the image, while stage clips hold the slide in place. |
| Add lens powers | Successive enlargement is multiplicative, so use the product of the eyepiece and objective powers rather than their sum. |
| Make a small length smaller when converting millimetres to micrometres | A micrometre is the smaller unit, so the numerical value becomes larger by a factor of one thousand. |
Try it
Which statements correctly describe the diaphragm of a compound light microscope? Select all that apply.
- It adjusts the amount of transmitted light.
- It sharpens the image by moving the stage greatly.
- It changes the power printed on an objective.
- Its setting can make the field brighter or dimmer.
A microscope uses a 10 times eyepiece and a 40 times objective. Enter the exact total magnification as a number.
A specimen is actually 0.02 millimetres long and its image is 5 millimetres long. Both measurements already use the same unit. What is the magnification?
- 100 times
- 250 times
- 500 times
- 0.004 times