Focal length of a convex lens will be maximum for
Focal length of a convex lens will be maximum for
- Green Light
- Blue Light
- Red Light
- Yellow Light
The Correct Option is C
Approach Solution - 1
The focal length of a convex lens is influenced by the refractive index of the material it is composed of and the wavelength of light passing through it. The refractive index of a material varies slightly with different wavelengths of light, which in turn affects the focal length.
In general, the refractive index of a material decreases as the wavelength of light increases. This phenomenon is known as dispersion. Among the options given, red light has the longest wavelength (longer than green, blue, and yellow light), so the refractive index of the lens material will be the least for red light.
According to the lens maker's formula, a lower refractive index corresponds to a longer focal length for a convex lens. Therefore, the focal length of a convex lens will be maximum for (C) red light.
Approach Solution -2
The focal length of a convex lens is influenced by the refractive index of the lens material, which can vary depending on the wavelength (or color) of light. This variation is referred to as chromatic aberration.
In general, the refractive index of a material is higher for shorter wavelengths, such as blue light, and lower for longer wavelengths, such as red light. Consequently, the focal length of a convex lens is shorter for shorter wavelengths and longer for longer wavelengths.
Given this information, the focal length of a convex lens will be maximum for red light. Red light has a longer wavelength compared to green, blue, and yellow light. Therefore, when red light is used, a convex lens will exhibit the maximum focal length.
Approach Solution -3
Focal length of a convex lens depends on the wavelength of the light due to dispersion.
Since refractive index decreases with increasing wavelength:
- Red light (longest wavelength) bends the least
- Blue light (shortest wavelength) bends the most
Hence, the lens has the maximum focal length for red light.
Correct answer: Red Light
Top Questions on Ray optics and optical instruments
- Two convex lenses A and B, each of focal length 10.0 cm, are mounted on an optical bench at 50.0 cm and 70.0 cm respectively. An object is mounted at 20.0 cm. Find the nature and position of the final image formed by the combination.
- CBSE CLASS XII - 2025
- Physics
- Ray optics and optical instruments
- A convex lens has focal length 20 cm. An object is placed at a distance of 40 cm from the lens. What is the position of the image formed?
- BITSAT - 2025
- Physics
- Ray optics and optical instruments
A current element X is connected across an AC source of emf \(V = V_0\ sin\ 2πνt\). It is found that the voltage leads the current in phase by \(\frac{π}{ 2}\) radian. If element X was replaced by element Y, the voltage lags behind the current in phase by \(\frac{π}{ 2}\) radian.
(I) Identify elements X and Y by drawing phasor diagrams.
(II) Obtain the condition of resonance when both elements X and Y are connected in series to the source and obtain expression for resonant frequency. What is the impedance value in this case?- CBSE CLASS XII - 2025
- Physics
- Ray optics and optical instruments
- An object is placed 30 cm from a thin convex lens of focal length 10 cm. The lens forms a sharp image on a screen. If a thin concave lens is placed in contact with the convex lens, the sharp image on the screen is formed when the screen is moved by 45 cm from its initial position. Calculate the focal length of the concave lens.
- CBSE CLASS XII - 2025
- Physics
- Ray optics and optical instruments
- An equiconvex lens is made of glass of refractive index 1.55. If the focal length of the lens is 15.0 cm, calculate the radius of curvature of its surfaces.
- CBSE CLASS XII - 2025
- Physics
- Ray optics and optical instruments
Questions Asked in KCET exam
- Identify the incorrect statement with respect to the rules of Binomial Nomenclature.
- KCET - 2025
- Nomenclature and taxonomy
- If the number of terms in the binomial expansion of \((2x + 3)^n\) is 22, then the value of \(n\) is:
- KCET - 2025
- Binomial theorem
You are given a dipole of charge \( +q \) and \( -q \) separated by a distance \( 2l \). A sphere 'A' of radius \( R \) passes through the centre of the dipole as shown below and another sphere 'B' of radius \( 2R \) passes through the charge \( +q \). Then the electric flux through the sphere A is
- KCET - 2025
- Electrostatic potential
- If \(N_2\) gas is bubbled through water at 293 K, how many moles of \(N_2\) gas would dissolve in 1 litre of water? Assume that \(N_2\) exerts a partial pressure of 0.987 bar. [Given \(K_H\) for \(N_2\) at 293 K is 76.48 K bar]
- KCET - 2025
- Gas laws
- A solenoid is 1 m long and 4 cm in diameter. It has five layers of windings of 1000 turns each and carries a current of 7 A. The magnetic field at the centre of the solenoid is
- KCET - 2025
- Magnetic Field
Concepts Used:
Ray Optics and Optical Instruments
Optics, deals with the determination of behaviour and the properties of light, along with its interactions with the matter and also with the instruments that are used to detect it.
Ray optics is also known as the geometrical optics and it is a branch of science which describes light propagation.
Reflection is the change in direction of light at an interface in-between two different media so that the wave-front returns into a medium from which it was originated.
Speed of light is the rate at which the light travels in free space.
A phenomenal change in image formed when the light is passed from one medium to another which is called Refraction.
Total Internal Reflection is the reflection of light when the light ray enters into a rarer medium from a denser medium and the angle of incidence is higher than the critical angle of incidence then that light ray will be reflected back to the denser medium.
Read More: Ray Optics and Optical Instruments