Light: Shadows and Reflections – Formula & Equation Sheet
Essential formulas and equations from Curiosity, tailored for Class 7 in Science.
This one-pager compiles key formulas and equations from the Light: Shadows and Reflections chapter of Curiosity. Ideal for exam prep, quick reference, and solving time-bound numerical problems accurately.
Key concepts & formulas
Essential formulas, key terms, and important concepts for quick reference and revision.
Formulas
Angle of Reflection = Angle of Incidence
This rule states that the angle at which light hits a reflecting surface (angle of incidence) is equal to the angle at which it reflects off (angle of reflection). Useful in understanding how mirrors work.
Speed of Light, c = 3 × 10⁸ m/s
Represents the speed at which light travels in a vacuum. It is fundamental in equations relating to optics and communication technologies.
Distance of Object = Distance of Image
In a plane mirror, the distance from the object to the mirror equals the distance from the mirror to the image, illustrating how reflections work.
Area of Shadow = Height of Object × Distance of Object
This formula provides insight into how the height of an object and its distance from the light source affect the size of its shadow.
Brightness = Power / Area
This expression showcases how the intensity of light diminishes as it spreads over a greater area, relevant when discussing brightness of light sources.
Refraction Law: n = sin(i) / sin(r)
Where n is the refractive index, i is the angle of incidence, and r is the angle of refraction when light passes from one medium to another.
Image Height / Object Height = Image Distance / Object Distance
This relationship describes how the sizes of images and objects relate in mirror systems.
Pinhole Camera Formula: h = H × d / D
Where h is the height of the image, H is the height of the object, d is the distance between the pinhole and the screen, and D is the distance between the object and the pinhole.
α (alpha) = tanθ
This expression relates the angle of elevation (θ) to the vertical height and horizontal distance in certain light path scenarios.
Illuminance (E) = I / d²
Where E is illuminance in lux, I is luminous intensity in candelas, and d is distance from the light source. This aids in understanding how light intensity decreases with distance.
Equations
V = fλ
Where V is the speed of light, f is frequency, and λ (lambda) is wavelength. This formula connects different characteristics of light waves.
Focal Length (f) = R / 2
Where R is the radius of curvature for concave and convex mirrors. This is crucial in lens and mirror calculations.
1/f = 1/v + 1/u
In lens formula, f is the focal length, v is the image distance, and u is the object distance, helping solve optics problems.
S = B × T
Where S is the shadow's area, B is the base area of the object, and T is the thickness of the object blocking the light.
Power = Voltage × Current
This expression relates to light sources, showing how electrical power is used to generate light.
n₁sinθ₁ = n₂sinθ₂
Snell's Law of Refraction, where n₁ and n₂ are refractive indices of the two media, and θ₁ and θ₂ are the angles of incidence and refraction.
Visual Angle = Size of Object / Distance
This equation helps understand how size and distance impact what we perceive with our eyes, relevant in optics.
i = a + b (for shadows)
Where i represents the intensity of the shadow, a is the obscure angle, and b is the direct light angle.
Reflected Ray = Incident Ray + Mirror Surface Normal
A basic understanding of the projection of rays indicates the direction in which light reflects off a surface.
E = hf
Where E is energy, h is Planck's constant, and f is frequency. This is relevant in calculating the energy of light photons.
