OCR A-Level Physics Module 6: Summary Paper and Study Guide

▪ capacitor - Anstwo overlapping plates separated by an insulator used to store charge ▪ dielectric - Ans an insulating material between the plates of a capacitor that can be polarised ▪ dielectric polarization - Anseach plate of the capacitor is charged causing the ends of the dielectric to become oppositely charged, keeping the charge from leaking out of the capacitor ▪ how the capacitor builds charge - Anselectron flows round the circuit in a current, reaches a plate and gives it a negative charge. this repels an electron from the opposite plate, causing an equal, opposite charge ▪ capacitance - Ansthe charge stored per unit potential difference, measured in Farads ▪ C=Q/V - Ansequation linking charge pd and capacitance ▪ C=ε₀A/d - Ansequation for capacitance determined by capacitor dimensions ▪ combining capacitors in series - Ans1/C₀ = 1/C₁ + 1/C₂ + 1/C₃ ▪ combining capacitors in parallel - AnsC₀ = C₁ + C₂ + C₃ ▪ energy stored in a capacitor - AnsW=½VQ ▪ time constant - Anstime taken for the charge on a capacitor to fall to 37% of its initial value ▪ Q=Q₀e^-t/RC - Anscharging equation for a capacitor ▪ half-life (capacitor) - Anstime taken for charge/pd/current across a capacitor to halve ▪ effect of increasing C on charging time - Ansa larger charge can be stored, making the time taken to charge up longer ▪ effect of increasing R on charging time - Anscurrent is reduced meaning charge takes longer to build up increasing charging time ▪ Q=Q₀(1-e^-t/RC) - Ansequation for charging a capacitor ▪ why current drops to zero when charging a capacitor - Ansthe pd across the capacitor increases exponentially. it has the opposite polarity to the power supply so its pd cancels out the power supply's causing the pd and therefore current to drop to zero. ▪ how a capacitor smooths AC current - AnsAC is input through a diode so current flows in one direction but with gaps. the capacitor charges when current flows and discharges when its stops, ensuring a smoother flow of current. ▪ field - Ansa region in space in which an object experiences a force ▪ electric field strength - Ansforce per unit positive charge ▪ E=F/Q - Ansequation linking force, electric field strength and charge ▪ coloumb's law - Ansthe force between two charged particles is directly proportional to the product of the charges, inversely proportional to the square of the separation and maximum when the charges are separated by a vacuum ▪ F=Qq/4πε₀r² - Ansequation for coulomb's law ▪ ε₀ - Anspermittivity of free space, 8.85×10⁻¹² Fm⁻¹ ▪ F=QV/d - Ansforce due to a uniform field ▪ electric potential energy - Answork done in moving two like charges togethe