3.6.2Stoichiometry
Real and Virtual Images — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions
5 min read 4 parts Lesson 13 of 28 Unit quiz
Curriculum Equation Key قوانين المول والحسابات الكيميائية - Moles & Stoichiometry FormulasFast Exam Solution
n = m / M_r | N = n × N_A (6.022 × 10²³) | M = n / V | V_gas = n × 22.4 L (STP)
Word Equation & Conditions: عدد المولات = الكتلة بالجرام ÷ الكتلة المولية | عدد الجسيمات = عدد المولات × عدد أفوجادرو
Location & Specifications: كيمياء التحصيلي وثانوي وبكالوريا و Cambridge IGCSE Chemistry.
Section 1 of 4Image Types
Whether an image is real or virtual depends on whether light actually converges at the image position.
Real image
- Real image Formed where light rays actually converge, so it can be projected onto a screen, and it is always inverted.
Virtual image
- Virtual image Formed where rays only appear to meet when traced backwards, so it cannot be projected and is always upright.
Projector example
- Projector example A projector lens forms a real image on a screen, which is why the picture can be seen by a whole audience.
Magnifying glass example
- Magnifying glass example A magnifying glass held close to text forms a virtual, upright and magnified image that can only be seen through the lens.
Section 2 of 4Image Position with a Convex Lens
Moving the object changes the image type, size and orientation.
1
With the object beyond 2f, a real, inverted and diminished image forms between f and 2f on the far side of the lens.
2
With the object exactly at 2f, a real, inverted image of the same size forms at 2f on the far side of the lens.
3
With the object between f and 2f, a real, inverted and magnified image forms beyond 2f on the far side of the lens.
4
With the object closer than f, a virtual, upright and magnified image forms on the same side of the lens as the object.
| Object position | Image type | Orientation | Size |
|---|---|---|---|
| Beyond 2f | Real | Inverted | Diminished |
| At 2f | Real | Inverted | Same size |
| Between f and 2f | Real | Inverted | Magnified |
| Closer than f | Virtual | Upright | Magnified |
Section 3 of 4Diverging Lens Images
Diverging Lens Images
Always virtual
- Always virtual A concave lens forms only virtual images, however far away the object is placed from the lens.
Always upright
- Always upright The virtual image from a concave lens is the same way up as the object, so it is never inverted.
Always diminished
- Always diminished The image from a concave lens is smaller than the object, so it appears to be shrunk.
Ray tracing
- Ray tracing Draw a ray through the centre and a ray parallel to the axis that appears to come from the focus, then trace both backwards.
Section 4 of 4Exam Checklist & Tips
3.6.2 – Key Points for the Exam
- Real image An image formed where light rays actually meet, which can be projected onto a screen.
- Virtual image An image formed where light rays only appear to meet, which cannot be projected onto a screen.
- Inverted Upside down compared with the object.
- Upright The same way up as the object.
- Ray diagram A scale drawing that uses principal rays to locate and describe an image.
Common Mistakes
- Saying a virtual image can be projected onto a screen; a virtual image cannot be captured on a screen.
- Describing any image seen through a lens as real; real images need light rays to actually converge.
- Ignoring the object position relative to the focal length when deciding whether the image is real or virtual.
- Drawing a virtual image on the far side of the lens rather than on the same side as the object.
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