Question:
Which of the following mirrors has a positive focal length?
Which of the following mirrors has a positive focal length?
Show Hint
Concave mirrors are used in torches, headlights, and solar cookers because they converge light at a real focus.
Updated On: Sep 19, 2025
- Convex mirror
- Plane mirror
- Concave mirror
- None of these
Hide Solution
Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Step 1: Conceptual Understanding:
The focal length ($f$) of a mirror is the distance between the pole and the focus. The sign convention determines whether $f$ is positive or negative.
Concave mirror: Focus is in front of the mirror → focal length is positive.
Convex mirror: Focus lies behind the mirror → focal length is negative.
Plane mirror: Focal length is considered infinite.
Step 2: Application:
Concave mirrors converge parallel rays to a real focus in front of them. Thus, according to the sign convention, their focal length is positive. Step 3: Final Answer:
The mirror with positive focal length is the Concave mirror.
The focal length ($f$) of a mirror is the distance between the pole and the focus. The sign convention determines whether $f$ is positive or negative.
Concave mirror: Focus is in front of the mirror → focal length is positive.
Convex mirror: Focus lies behind the mirror → focal length is negative.
Plane mirror: Focal length is considered infinite.
Step 2: Application:
Concave mirrors converge parallel rays to a real focus in front of them. Thus, according to the sign convention, their focal length is positive. Step 3: Final Answer:
The mirror with positive focal length is the Concave mirror.
Was this answer helpful?
0
0
Top Questions on Optics
- A thin convex lens of focal length \( 5 \) cm and a thin concave lens of focal length \( 4 \) cm are combined together (without any gap), and this combination has magnification \( m_1 \) when an object is placed \( 10 \) cm before the convex lens.
Keeping the positions of the convex lens and the object undisturbed, a gap of \( 1 \) cm is introduced between the lenses by moving the concave lens away. This leads to a change in magnification of the total lens system to \( m_2 \).
The value of \( \dfrac{m_1}{m_2} \) is
- A thin prism with angle 5° of refractive index 1.72 is combined with another prism of refractive index 1.9 to produce dispersion without deviation. The angle of second prism is :
The strain-stress plot for materials A, B, C and D is shown in the figure. Which material has the largest Young's modulus?
- When you look at an object very close to your eyes, the:
- A convex lens of focal length 15 cm, is forming a real image. If the size of image is same as the size of object, then position of object and position of image will be, respectively :
View More Questions
Questions Asked in Bihar Class X Board exam
- Why is sports important for children?
- Bihar Board X - 2026
- Food and Nutrition
- Which of the following is a family budget?
- Bihar Board X - 2026
- Home Science
- Which of the following is an excretory organ of the human body?
- What should be the quality of a first aider ?
- Bihar Board X - 2026
- Home Science
- Which disease is caused by iron deficiency?
- Bihar Board X - 2026
- Food and Nutrition
View More Questions