1. Light – Reflection and Refraction
Reflection: Jab light kisi polish surface (mirror) se takra kar wapas aati hai.
Mirror Formula: $\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$
Magnification ($m$): $m = \frac{h'}{h} = -\frac{v}{u}$
Refraction: Jab light ek medium se dusre medium mein jati hai aur mud jati hai.
Snell's Law: $\frac{\sin i}{\sin r} = \text{constant}$ (Refractive Index).
Lens Formula: $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
Power of Lens ($P$): $P = 1/f$ (in meters). Unit: Dioptre (D).
2. The Human Eye and the Colourful World
Power of Accommodation: Aankh ki lens ka apni focal length ko adjust karne ki kshamta.
Defects of Vision:
Myopia (Near-sightedness): Door ka nahi dikhta. Corrected by Concave Lens.
Hypermetropia (Far-sightedness): Paas ka nahi dikhta. Corrected by Convex Lens.
Dispersion: White light ka 7 rangon (VIBGYOR) mein tootna jab wo Prism se guzarti hai.
Atmospheric Refraction: Iske karan taare timtimate (twinkling of stars) hain.
3. Electricity (Vidyut)
Electric Current ($I$): Flow of charge. $I = Q / t$. Unit: Ampere (A).
Ohm’s Law: $V = IR$ (Potential difference is proportional to current).
Resistance ($R$): $R = \rho \frac{l}{A}$. Unit: Ohm ($\Omega$).
Resistors in Series: $R_s = R_1 + R_2 + R_3$
Resistors in Parallel: $\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$
Heating Effect (Joule's Law): $H = I^2Rt$.
4. Magnetic Effects of Electric Current
Magnetic Field: Current wale wire ke aas-paas ka area jahan magnetic force feel ho.
Right-Hand Thumb Rule: Magnetic field ki direction pata karne ke liye.
Solenoid: Ek coil jo magnet ki tarah behave karti hai jab usme current flow hota hai.
Electromagnetic Induction: Jab magnetic field badalne se current paida ho (Generator ka principle).
Fleming’s Left-Hand Rule: Motor ke liye use hota hai.