10 Electromotive ForceDifference in electric potential between the terminalsCalled emfElectron flow begins instantly, but is very slow
11 Resistance and Ohm’s Law Opposition to the flow of electronsLike Friction for electricityOhm’s LawV = IRV = Potential Difference (V)I = Current (A)R = Resistance (Ω)
12 ExampleA potential difference of 24 V is applied to a 150 Ω resistor. How much current flows through the resistor?
13 ResistivityThe quality of that characterizes the resistance of a given material.Represented as ρThe greater the resistivity, the greater the resistance
14 Resistance Formula Example: R = ρ (L/A) R = Resistance (Ω)ρ = Resistivity (Ω • m)L = Length of wire (m)A = Cross-sectional area of wire (m2)Example:A current of 1.82 A flows through a copper wire 1.75 m long and 1.10 mm in diameter. Find the potential difference between the ends of the wire. The resistivity of copper is 1.68 x 10-8 Ω•m
15 Temperature Dependence and Superconductivity As electrons move, the conductor become hotThe hotter the conductor, the more resistivity due to increased Kinetic EnergySuperconductorConducts with little or no resistivityMust be at very low temperatures
16 Electric Power Rate of change of energy Formula Example P = W/t P = IV P = Power (W)I = Current (A)V = Potential Difference (V)ExampleA handheld electric fan operates on a 3.00 V battery. If the power generated by the fan is 2.24 W, what is the current supplied by the battery?
17 Power dissipated in a resistor P = V2/RP = Power (W)V = Potential Difference (V)R = Resistance (Ω)ExampleA battery with an emf of 12 V is connected to a 545 Ω resistor. How much energy is dissipated in the resistor in 65s?
18 Energy UsageKilowatt hours are used by electric companies to bill for energy usage.1kWh = 3.6 x 106 JExampleA holiday goose is cooked in the kitchen oven for 4.00 hr. Assume that the stove draws a current of 20.0 A, operates at a voltage of V, and uses electrical energy that costs $0.048 per kWh. How much does it cost to cook your goose?
19 Household CircuitsA household circuit can become overloaded if too much current flows through the circuit than is considered safeCircuit breakers and fuses are installedThey act as switches and break the current when the current becomes too large.
20 Resistors in Series Equivalent Resistance Series Circuit Total Resistance for a circuitSeries CircuitResistors connected one after anotherAll resistors have the same currentPotential Difference across the resistors must sum to the emf of the batteryReq = R1 + R2 + R3 …
21 Example ProblemA circuit consists of three resistors connected in series to a 24.0 V battery. The current in the circuit is A. Given that R1 = Ω and R2 = Ω, find (a) the value of R3 and (b) the potential difference across each resistor.
22 Resistors in Parallel Parallel Circuit Connected across the same potential difference.The total current is the sum of all the individual currentsPotential difference is the same across each resistor1/Req = 1/R1 + 1/R2 + 1/R3 …
23 ExampleConsider a circuit with three resistors , R1 = Ω, R2 = Ω, and R3 = Ω, connected in parallel with a 24.0 V battery. Find (a) the total current supplied by the battery and (b) the current through each resistor.
24 Combination CircuitsIn the circuit shown in the diagram, the emf of the battery is 12.0 V, and all the resistors have a resistance of 200 Ω. Find the current supplied by the battery to this circuit.
25 Kirchhoff’s Rules The Junction Rule Charge conservation The current entering any point in a circuit must equal the current leaving that pointThe algebraic sum of the currents should equal zero+ current going into the point, - current going out of the point
26 The Loop Rule Energy Conservation The algebraic sum of all potential differences around a closed loop in a circuit is zero.Example Problem
27 Capacitors in Parallel Equivalent Capacitance is the sum of all the capacitors.ΣC = C1 + C2 + C3 …ExampleTwo capacitors, one 12.0μF and the other of unknown capacitance are connected in parallel across a battery with an emf of 9.00 V. The total energy stored in the two capacitors is J. What is the value of the capacitance C?
28 Capacitors in Series Σ1/Ceq = 1/C1 + 1/C2 + 1/C3 … Example Consider the electrical circuit drawn, consisting of a 12 V battery and three capacitors connected partly in series and partly in parallel. Find (a) the equivalent capacitance of this circuit and (b) the total energy stored in each capacitor.
29 AmmeterDesigned to measure the current in a particular part of a circuit.Must be hooked up in series
30 Voltmeter Measures the potential difference across two points Must be in parallel to the circuit.