Science 9: Unit D – Topic 2 Notes Current Electricity

What is a circuit? A pathway that provides a continuous path for an electric current to move through. A pathway that provides a continuous path for an electric current to move through.

Circuit Diagrams A simple circuit contains three parts: A simple circuit contains three parts: 1. A voltage source, usually a battery cell. 1. A voltage source, usually a battery cell. 2. One or more resistors/loads. 2. One or more resistors/loads. 3. A pathway for the current to move through. 3. A pathway for the current to move through.

Circuit Symbols A straight line represents conducting wire. A straight line represents conducting wire. The following symbol represents a cell. The following symbol represents a cell. The following symbol represents a resistor/load. The following symbol represents a resistor/load. This symbol represents an on-off switch. This symbol represents an on-off switch. The following symbol is also used for a load such as a lamp or appliance which does useful work. The following symbol is also used for a load such as a lamp or appliance which does useful work.

What is Current? Electric charge is measured in a unit called a coulomb. (unit symbol = C). Electric charge is measured in a unit called a coulomb. (unit symbol = C). - Electric Current (I) – a stream of electrons moving through a circuit. -The speed of the current depends on a number of factors including the voltage (amount of energy) of the electrons, resistance of the pathway, temperature, etc. - The unit for current is called the ampere (symbol = A)

Measuring Current Galvanometer – device used to measure weak electric currents. Galvanometer – device used to measure weak electric currents. Ammeter – used to measure larger currents. Ammeter – used to measure larger currents. Because most currents are weak, galvanometers are used more frequently. Because most currents are weak, galvanometers are used more frequently.

Potential Difference/Voltage Energy used for pushing electrons in a current comes from cell where the positively charged part of the cell is connected to the negative end by a circuit. (Remember because electrons are negative, they want to reach the positive end). Energy used for pushing electrons in a current comes from cell where the positively charged part of the cell is connected to the negative end by a circuit. (Remember because electrons are negative, they want to reach the positive end).

PD/Voltage Continued Potential Difference (V) – the difference in energy of the electricity between one part of the circuit and another part, usually after the current has passed through a load. Potential Difference (V) – the difference in energy of the electricity between one part of the circuit and another part, usually after the current has passed through a load. Another term for potential difference is voltage. Another term for potential difference is voltage. The unit for voltage is the volt (V). The unit for voltage is the volt (V). Voltage is measured by a device called a voltmeter. Voltage is measured by a device called a voltmeter.

Voltage usually means the energy the electrons are moving with. This is hard to measure directly in a circuit. Usually when we’re talking about voltage we’re just talking about batteries. and cells. Voltage usually means the energy the electrons are moving with. This is hard to measure directly in a circuit. Usually when we’re talking about voltage we’re just talking about batteries. and cells. Instead, what’s easier to measure is the DIFFERENCE in energy the current has before and after traveling through a resistor/load. Instead, what’s easier to measure is the DIFFERENCE in energy the current has before and after traveling through a resistor/load. Why is voltage called potential difference? It’s because we measure the difference in ELECTRICAL POTENTIAL ENERGY the electron current has before and after going through the load. Why is voltage called potential difference? It’s because we measure the difference in ELECTRICAL POTENTIAL ENERGY the electron current has before and after going through the load. If the electron current has a voltage of 120 V coming into a plasma HDTV and a voltage of 60 V coming back into the socket then we can say that the TV has a PD of 60 V. If the electron current has a voltage of 120 V coming into a plasma HDTV and a voltage of 60 V coming back into the socket then we can say that the TV has a PD of 60 V.

How do we measure PD of various devices? By attaching a voltmeter to the circuit. Two wires are attached from the voltmeter to the circuit. One wire is attached on either side of the resistor. How do we measure PD of various devices? By attaching a voltmeter to the circuit. Two wires are attached from the voltmeter to the circuit. One wire is attached on either side of the resistor.