Karnataka II PUC Physics (KSEAB) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Coulomb's law

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance between them, acting along the line joining them.

Electric dipole moment

A vector p = q × 2a pointing from the negative to the positive charge. It determines the torque pE sinθ experienced in a uniform field and the 1/r³ field far away.

Gauss's law

The total electric flux through any closed surface equals the enclosed charge divided by ε₀. Charges outside the surface contribute zero net flux through it.

Electric potential

The work done per unit positive charge in bringing a test charge from infinity to a point, with zero at infinity. It is a scalar and equals kq/r for a point charge.

Capacitance of parallel plates

C = ε₀A/d for air between plates of area A separated by d. Inserting a dielectric of constant K filling the gap multiplies the capacitance by K.

Energy stored in capacitor

A charged capacitor stores U = ½CV² = ½QV = Q²/2C. With a battery connected, inserting a dielectric increases stored energy by factor K; isolated, energy falls by K.

Drift velocity

The average velocity with which free electrons move opposite the field in a conductor, v_d = I/(nAe). It is very small, though the current appears almost instantly.

Wheatstone bridge balance

The bridge is balanced when P/Q = R/S and the galvanometer shows no deflection. The metre bridge uses this with unknown R = S·l/(100−l).

EMF and terminal voltage

For a cell of emf ε and internal resistance r, terminal voltage is V = ε − Ir while discharging and V = ε + Ir while charging. Maximum power transfer occurs at R = r.

Radius of circular path

A charge moving perpendicular to a magnetic field follows a circle of radius r = mv/(qB). The period T = 2πm/(qB) does not depend on the speed.

Ampere's circuital law

The line integral of B around a closed loop equals μ₀ times the net current passing through the loop. It gives B = μ₀nI inside a long solenoid.

Torque on current loop

A loop of N turns, area A, current I in field B experiences τ = NIAB sinθ = MB sinθ, where M = NIA is the magnetic moment.

Curie law

Above the Curie temperature, the magnetic susceptibility of a paramagnetic material is inversely proportional to absolute temperature, χ ∝ 1/T, because thermal agitation randomises the dipoles.

Lenz's law

The direction of an induced current is such that it opposes the change in magnetic flux that produced it. This is a statement of energy conservation in electromagnetic induction.

Resonance in series LCR

Resonance occurs at ω₀ = 1/√(LC), where X_L = X_C. Impedance then equals R, current is maximum, and the circuit behaves as purely resistive with power factor one.

Transformer equation

For an ideal transformer V_s/V_p = N_s/N_p = I_p/I_s, so power is conserved. A step-up transformer raises voltage and lowers current; laminated cores reduce eddy currents.

Speed of electromagnetic waves

In vacuum all electromagnetic waves travel at c = 1/√(μ₀ε₀) ≈ 3×10⁸ m/s. In a medium the speed is v = c/n, where n is the refractive index.

Displacement current

Maxwell introduced I_d = ε₀ dΦ_E/dt to complete Ampere's law, making it consistent for a charging capacitor. It predicts that changing electric fields produce magnetic fields.

Critical angle

The angle of incidence in the denser medium for which the refracted ray grazes the surface, given by sin C = 1/n. Beyond it, total internal reflection occurs.

Lens maker's formula

1/f = (n−1)(1/R₁ − 1/R₂) relates a thin lens's focal length to its refractive index and radii of curvature. Power P = 1/f is measured in dioptres.

Minimum deviation of prism

At minimum deviation the ray passes symmetrically, so n = sin[(A+D_m)/2]/sin(A/2). Dispersion occurs because n depends on wavelength, violet bending most.

Fringe width in double slit

The separation between adjacent bright or dark fringes is β = λD/d, where D is the slit-to-screen distance and d the slit separation. It increases with wavelength.

Brewster's law

At the polarising angle of incidence, tan i_p = n, and the reflected ray is completely polarised perpendicular to the plane of incidence. The reflected and refracted rays are then perpendicular.

Malus's law

When plane-polarised light of intensity I₀ passes through an analyser whose axis makes angle θ with the polariser, the transmitted intensity is I = I₀ cos²θ.

Photoelectric equation

Einstein's relation hν = hν₀ + ½mv²_max gives the maximum kinetic energy of photoelectrons. The stopping potential satisfies eV₀ = hν − hν₀.

de Broglie wavelength

Every moving particle has an associated wavelength λ = h/p = h/(mv). For an electron accelerated through V volts, λ is about 12.27/√V Å.

Bohr radius and energy

For hydrogen, r_n = 0.53 n² Å and E_n = −13.6/n² eV. The ionisation energy from the ground state is therefore 13.6 eV.

Half-life

The time in which half the radioactive nuclei decay, T½ = 0.693/λ. After n half-lives a fraction (1/2)ⁿ of the original sample remains undecayed.

Binding energy per nucleon

BE = Δm c² (1 u = 931.5 MeV) divided by mass number. It peaks near iron at about 8.8 MeV, so both fission of heavy and fusion of light nuclei release energy.

Depletion layer

The charge-free region at a p-n junction containing immobile ions, which creates a barrier potential of about 0.7 V in silicon and 0.3 V in germanium.

Zener diode regulation

Operated in reverse breakdown, a Zener diode maintains a nearly constant voltage across its terminals despite current changes, so it is used to regulate supply voltage.

Vernier callipers least count

Least count equals one main-scale division divided by the number of vernier divisions, commonly 0.1 mm. Zero error, if present, is applied with the opposite sign to the reading.