Free QCE Physics Flashcard Review
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Define centripetal acceleration.
Centripetal acceleration is the acceleration directed toward the centre of a circular path, required to keep an object moving in a circle. Magnitude: a_c = v2/r = ω2r. SI unit: m s-2.
State Newton's Law of Universal Gravitation.
F = GMm/r2, where G = 6.67 × 10-11 N m2 kg-2. Forces are in newtons, masses in kg, r in metres.
Define gravitational field strength.
g = F/m = GM/r2. SI unit: N kg-1 or m s-2. At Earth's surface, g ≈ 9.8 m s-2.
State Kepler's First Law.
The orbit of every planet is an ellipse with the Sun at one of the two foci.
State Kepler's Second Law.
A line joining a planet to the Sun sweeps out equal areas in equal times. Planets move faster when closer to the Sun.
State Kepler's Third Law.
T2 ∝ r3 or T2 = (4π2/GM) × r3, where T is period (s), r is orbital radius (m).
Derive the formula for orbital speed.
GMm/r2 = mv2/r, so v = √(GM/r). SI unit: m s-1. Orbital speed decreases with increasing radius.
State Coulomb's Law.
F = kQ1Q2/r2, where k = 8.99 × 109 N m2 C-2. F in newtons, Q in coulombs, r in metres.
Define electric field strength.
E = F/Q = kQ/r2 (for a point charge). SI unit: N C-1 or V m-1. Direction away from positive charge, toward negative charge.
Define electric potential and potential difference.
V = E_p/Q or V = W/Q. Potential difference U = V1 - V2. SI unit: volts (V) or J C-1. For a point charge: V = kQ/r.
Derive the relationship between electric field strength and potential difference.
E = -ΔV/Δr (for uniform fields). Rearranging: U = E × d, where d is perpendicular distance. Unit: 1 N C-1 = 1 V m-1.
State the formula for magnetic force on a current-carrying conductor.
F = BIL sin(θ), where B is flux density (tesla, T), I is current (amperes, A), L is length (m). Maximum force when θ = 90°: F_max = BIL.
State the formula for magnetic force on a moving charged particle.
F = Bqv, where B is flux density (tesla, T), q is charge (coulombs, C), and v is velocity (m s-1). Direction given by right-hand rule. SI unit: newtons (N).
Explain the motor effect and state the direction rule.
Motor effect: current-carrying conductor in a magnetic field experiences a force, causing rotation. Fleming's Left-Hand Rule: Thumb = force, First finger = magnetic Field (N to S), seCond finger = Current.
Define magnetic flux.
Φ = BA cos(θ), where B is flux density (tesla, T), A is area (m2), θ is angle between B and normal to area. SI unit: weber (Wb), where 1 Wb = 1 T m2.
State Faraday's Law of Electromagnetic Induction.
ε = -N(ΔΦ/Δt), where N is number of turns, ΔΦ/Δt is rate of change of flux (Wb s-1). SI unit: volts (V). The negative sign indicates direction (Lenz's Law).
State Lenz's Law.
The direction of an induced current or EMF opposes the change in magnetic flux that produced it. An induced current creates a magnetic field opposing the original change.
Derive the formula for induced EMF in a moving conductor.
ε = BLv, where L is conductor length, v is velocity perpendicular to magnetic field B. Derivation: EMF = work done per unit charge = (Bqv·L)/q = BLv. SI unit: volts (V).
State the transformer equation.
V_p/V_s = N_p/N_s = I_s/I_p, where V_p and V_s are primary and secondary voltages, N_p and N_s are turns, I_p and I_s are currents. Power is conserved: V_p I_p = V_s I_s.
Define the gravitational constant G and state its SI units.
G is the proportionality constant in Newton's Law: F = GMm/r2. Value: G = 6.67 × 10-11 N m2 kg-2 (or m3 kg-1 s-2). Same value throughout the universe.