NCEA level 3: Physics - electricity: full Questions with 100% Correct Answers

-ve sign is used to state Lenz law - ε oppose change change in Φ inside loop Additional capacitor in parallel - Like adding more A to the first capacitor so more Q can be stored Alternating current (AC) - Produces V and I that vary with time. Polarity of V and direction of I regularly reverses. Supply f gives no of ω (angular frequency) cycles of this reversal in polarity or direction per sec. ω = 2πf Applying Kirchhoff's Voltage law through a power supply - When moving through a power supply: -from -ve terminal to +ve terminal is V gain, so +ve voltage -from +ve terminal to +ve terminal is V lost, so -ve voltage Applying Kirchhoff's Voltage Law through a resistor - When moving though a resistor: -If same direction as I, V is lost so -ve voltage -If opposite direction as I, V is gained so +ve voltage Ca - C with air or vacuum between plates Calculation of Φ when not perpendicular to magnetic field - Φ = BA x cosθ Calculation of Φ when perpendicular to magnetic field - Φ = BA Capacitance (C) - Measure of how much charge a capacitor can hold for each 1 Volt applied across capacitor. Measured in farad (F)Capacitor fully charged when: - Flow of e- (current) stops when, V across capacitor = V of supply Capacitor in series - Adding capacitors will reduce total circuit C i.e This change will reduce ability of circuit to store Q Capacitors - consists of 2 parallel metal plates separted by distance d (m) Usually these plates have an insulating layer (a dielectric) between them Capacitors in AC circuits - Alternating I repeatedly charges and discharges capacitor causes alternating V drop Vc across capacitor Capacitors in Parallel - Adding capacitors increase total circuit C i.e Change will increase ability of circuit to store Q. Capacitors purpose - Store electric charge and electric energy Cd - C with dielectric Charging a capacitor - Connected to a power supply, Q flows quickly onto the capacitor's plates (high I). As Q builds up on plates, charges flow more and more gradually (lower I) Coventional current - In opposite direction to eCT is doubled - In parallel τ doubles a more Q needs to flow on to the plates. So takes longer time for capacitor to charge CT is halfed - In series τ is halfed as less Q needs to flow on to the plates.Takes a shorter time for circuit to reach max Q Decreasing A of the plates - Decreasing C of capacitor