Draw ray diagrams for convex mirrors
Scenario
Car ke side-view mirror mein dekha hai? Badi badi trucks aur cars bilkul chhoti chhoti dikhai deti hain.
Ek chhota sa mirror peeche ki itni saari badi cheezon ko apne andar kaise fit kar leta hai?
Mental model
Convex = Humesha chhota, humesha seedha.
Convex mirror kisi bhi object ko dekhe, uska ek hi kaam hai: image ko chhota karna aur mirror ke andar seedha (erect) khada karna. Isliye piche se aati kitni bhi badi gaadi ho, uska mini-version ban jata hai.
Explanation
Convex mirror ki surface bahar ko ubhri (bulging) hoti hai. Iska Focus (F) aur Centre of Curvature (C) dono mirror ke peeche hote hain. Kyunki light mirror ke peeche nahi ja sakti, isliye saari images Virtual banti hain.
Convex mirror mein sirf 2 cases hote hain. Pehla, jab object infinity (bahut door) par ho. Rays parallel aati hain aur diverge (bikharti) ho jati hain. Dotted lines se peeche extend karne par woh F par milti hain. Image point-sized (bahut choti) aur virtual banti hai.
Doosra case: jab object mirror ke samne kisi bhi finite distance par ho (paas ya thoda door). Parallel ray diverge hogi aur lagayega ki F se aa rahi hai. Centre (C) ki taraf point karne wali ray waise hi bounce back hogi. Ye dono dotted lines P aur F ke beech intersect karti hain. Result? Ek diminished (choti), virtual, aur erect (seedhi) image.
Kyunki yeh hamesha choti aur seedhi image banata hai, iska 'field of view' (dekhne ka area) bahut bada ho jata hai. Isiliye gaadiyo mein rear-view mirror aur shops mein security mirrors ke roop mein convex mirrors hi use hote hain.
Worked example
Problem: A car is at a distance of 10 m from a convex rear-view mirror. Where will its image form conceptually?
- Kisi bhi distance ke liye, convex mirror hamesha pole aur focus ke beech peeche image banata hai.
Answer: Between the pole (P) and focus (F) behind the mirror.
Problem: Can a convex mirror ever form a real and inverted image?
- Convex mirror light rays ko diverge karta hai, isliye wo aage kabhi nahi milti.
- Wo sirf mirror ke peeche milti hui lagti hain.
Answer: No, it always forms virtual and erect images.
Key points
- Image Nature: Always Virtual and Erect.
- Image Size: Always Diminished (smaller than object).
- Field of View: Wider field of view, making it ideal for rear-view mirrors.
Common mistakes
- Drawing enlarged virtual images: Virtual image sunte hi kuch students concave wala (enlarged) yaad kar lete hain. Convex ki virtual hamesha chhoti hoti hai.
Recall questions
- What is the size of the image formed by a convex mirror compared to the object?
- Why is a convex mirror used as a rear-view mirror?
- Can a convex mirror form a real image?
Questions & answers
A full length image of a distant tall building can definitely be seen by using which type of mirror?
Convex mirror
Approach: Only a convex mirror provides a highly diminished, erect image of large objects over a wide field.
Why is a convex mirror used as a rear-view mirror in vehicles?
Because it always gives an erect, diminished image and provides a wider field of view.
Approach: Mention the two main advantages: erect image and wider field of view.
Continue learning
Previous: Define principal focus and focal length