Current Electricity SNC Grade 9

A Simple Circuit Load/Resistance Connecting wires Power source

Circuit diagrams Circuit Models

Introducing Some terms Current: represented by the symbol (I) Charge: represented by the symbol (Q) Coulomb: represented by the symbol (C) Ampere: represented by the symbol (A) Time: represented by the symbol (s)

Measuring Current Current is the flow of electrons It is measured with an ammeter Current (I) is measured in amps (A)

Current in Household Appliances ApplianceCurrent (A) Radio W lamp0.8 Colour TV1.7 Toaster8.8 Microwave oven11.7 Electric kettle12.5 Electric stove40

Electric Shock Electricity can Kill Use it safely Caution: Electrical Hazard

Charge Charge is measured in coulombs. 1 coulomb = 6.25 X electrons Current = charge moving past a point time I = Q t

Example: GRASS Method If 240C of charge pass a point in a conductor in 5.0 mins, What is the current through that point in the conductor? Given: Q = 240C, t= 5.0 mins Required: Current (I) in Amperes Analysis: Use the formula I = Q t Convert time from minutes to seconds = 5.0 x 60 = 300s Solution: I = 240 C = 0.80A 300 s Paraphrase: When 240C of charge pass a point in a conductor every 5.0 minutes, the current in the conductor is 0.80A

Batteries Are portable power sources Can be wet cells or dry cells Come in a variety of shapes & sizes Have different voltages

How a battery works

Changing energy from one form to another A battery changes chemical energy into electrical potential energy. This energy is used to move electrons through a circuit. A battery works like a pump

The battery “pumps” the electrons around the circuit.

Measuring the “pump” The pressure that the battery pumps the electrons around the circuit is called Voltage. (volts) and is measured with a voltmeter connected in parallel to the load or the battery.

Types of Circuits Series circuit. – the electricity has only ONE path.

Parallel Circuit – the electricity has a choice of paths.

Electricity is like grade 9 science students. It always takes the easiest path to get to the goal

The combined resistance RO in this circuit is equal to the sum of individual resistance R1 and R2. In other words: The total resistance (RO) is equal to the sum of all resistances (R1 + R2 + R ) SERIES CIRCUIT CALCULATIONS If, for example, two or more lamps (resistances R1 and R2, etc.) are connected in a circuit as follows, there is only one route that the current can take. This type of connection is called a series connection. The value of current I is always the same at any point in a series circuit.

SymbolComponentUnit of measurement AmmeterAmperes CellVolts Resistor Ohms Ω Switch X Voltmeter Volts V Connector X Circuit Symbols

Make the following A series circuit with 3 bulbs, a switch and power source. Draw the circuit diagram What do you notice about the brightness of the bulbs? Unscrew one bulb what happens?

AND.. A parallel circuit with 3 bulbs, 3 switches – one for each bulb, and power source. What do you notice about the brightness of the bulbs? Unscrew one bulb, what happens?

Electricity terms and formulae TermSymbolUnitFormulaDefinition Current I Ampere (amps) I = Q t Flow of electrons past a given point in a given time Potential Difference VVoltsV= Resistance ΩOhmsR = V I Power WWattsP = E t ChargeQCoulombsQ =I X t Efficiency% efficiency=

Ohm’s Law Resistance = Potential Difference (V) Current (A) R = V I symbol for resistance is Ω

If the potential difference of 1 volt causes a current of 1amp to flow then the resistance is 1 Ω. Ohm's Law deals with the relationship between voltage and current in an ideal conductor. This relationship states: The potential difference (voltage) across an ideal conductor is proportional to the current through it.

This graph shows a linear relationship between voltage and current. This resistor would be said to follow Ohm’s law. Resistance can be determined by using: Slope = Rise Run

You practice.. Use the data provided to create a graph of voltage vs. Current, with current plotted on the x-axis. Potential Difference (V) (V) Electric Current (I) (1mA = 1 X A)

Describe the shape of the graph Is the resistor shown on the graph an ohmic or a non-ohmic resistor? Explain.