Circuits AP PHYSICS 1 Circuit Diagrams Circuit diagrams

Circuits AP PHYSICS 1

Circuit Diagrams Circuit diagrams are used to show different components are connected in a circuit Symbols are used to represent the components, which are connected by horizontal and vertical lines, representing wires

Circuit Diagram

battery energy. - a device that converts chemical potential energy into electrical • Allesandro Volta constructed one of the first practical batteries. • He used zinc and copper electrodes in a weak sulfuric acid solution. circuit - any complete loop consisting of wires and electrical devices ex: batteries and light bulbs. anode (+) - the positive terminal of a battery. cathode (-) - the negative terminal of a battery. electric current direct current (dc) direction, from negative - the net rate at which charge flows past a given point. - in a battery circuit, the electrons can only flow in one terminal to positive terminal.

Voltmeter voltmeter - a high resistance device used to measure voltage. The symbol for a voltmeter is a circle with a V inside it.

Ammeter ammeter - -a low resistance device to measure current. to The circuit symbol for an ammeter is a circle with an A inside it. • Current is the same for any resistors in series with one another. So, if you’re going to measure the current through a resistor, the ammeter must be in series with the resistor whose current you want to measure. • The ammeter does not appreciably affect the current measurement due to its low resistance.

Electric current = the flow of electric charge from one place to another I = Δq/Δt I = current (Ampere = C/s, A) Δq Δt = flow of charge (C) = time interval (s) Two types of current: Direct current = current always flows in the same direction, provided by batteries Alternating current = current continuously reverses direction, provided by electrical outlets

Voltage Two requirements for current to flow: A closed conducting path = circuit A difference in electric potential Voltage = electric potential energy per unit of charge (aka EMF, potential difference) A battery is a source of voltage because it has an electric potential difference between its two terminals (Conventional) current in a circuit flows from the positive terminal of a battery to the negative terminal

Resistance = the hindrance to the flow of charge through a conductor in a circuit R = ρl/A R = resistance (Ohms, Ω) ρ (rho) = resistivity (Ωm) l = length of the conductor (m) A = cross-sectional area of the conductor (m 2) Resistance is also directly proportional to the temperature of the conductor

Factors that Influence Resistance

Ohm’s Law gives the relationship between current, voltage, and resistance in a circuit I = ΔV/R I = current (A) ΔV R = voltage (Volts, V) = resistance (Ω) Ohm’s Law can be applied to an individual conductor, a section of a circuit, an entire circuit, and any type of circuit

Series Circuits • The current only has one pathway to follow. • IF one section goes out the entire circuit does not work. • Current is the same at each point in the circuit

Voltage in Series Circuits When batteries are in series you add them together.

Resistors in Series

Resistance in Series If the resistors are in a series you will add them up to find total resistance. When another resistor (light bulb) is added in series, the total resistance increases. When resistance increases, current will decrease. Decreased current means dimmer light.

Current in Series To find the total current you will need to use the total voltage, total resistance, and Ohm’s Law to find the current moving through a circuit.

Parallel Circuit • Has at least one point where current divides • More than one path for current to flow • Paths are also known as branches

Voltage in Parallel If the batteries are in series you will add them together, just as it would be done with a series circuit.

Voltage In Parallel The total voltage will travel down each of the branches, equally.

Resistors in Parallel When the resistor are in parallel the reciprocal ( 1/R ) value of the individual resistances are all added together instead of the resistances themselves

Resistors in Parallel

Adding Resistors in Parallel When you add resistors in parallel circuits, you increase the total current.

Current in Parallel To find current in parallel circuits, you need to treat each branch like its own series circuit. Then add the currents for each branch together to find the total current.

Combination Circuits A third type of circuit involves the dual use of series and parallel connections in a circuit; such circuits are referred to as compound circuits or combination circuits.

Solving Combination Circuits In order to find resistance, voltage, and current in combination circuits you will have to convert the circuit into a series circuit.

Combination Circuit Example On Separate Sheet

Electrical Power = the rate at which electrical energy is dissipated by a conductor or circuit P = I ΔV P = power (W) I = current (A) ΔV = voltage (V) Just like Ohm’s Law, it can be applied to an individual conductor, a section of a circuit, an entire circuit, and any type of circuit

Kirchoff’s Rules For more complex circuits, Kirchoff’s rules are used to find the currents and voltages Kirchoff’s rules are based on conservation of charge (current) and energy (voltage) Junction rule = the algebraic sum of all currents meeting at any junction in a circuit must equal zero (incoming current equals outgoing current) Problem-solving tip: Arbitrarily choose a direction for the unknown current(s)- if the current turns out negative, it flows in the opposite direction

Kirchoff’s Rules Loop rule = the algebraic sum of all potential differences around any closed loop in a circuit is zero You will most likely have multiple equations to solve simultaneously Problem-solving tips: Potential difference across a resistor in the direction of the current is negative, opposite the current is positive. Potential difference across a battery from positive to negative terminal is negative, from positive to negative terminal is positive.

Kirchoff’s Rules