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Week 2 Electricity and circuits

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For centuries people have used the energy of flowing water to help them do work. What are the limitations of using water for energy?

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Would it work to put a water wheel in this pond?

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Dams allow better control over the flow of water

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There are some similarities between using water for useful work and using electricity for useful work.

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Electric current is the flow of electrons The amount of flow or current (I) is measured in amperes (A or amps) Current must flow through something going somewhere.

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Current is measured using an ammeter.

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Voltage (E) is the Electromotive force that makes the electrons move. Voltage is measured in volts (V) and the measurement is made by comparing one point to another reference point..

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It helps to understand electricity if we compare it to flow of water. Energy can be stored in water by pumping it up to a higher elevation.

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Gravity is the force exerted on the water trying to pull it back down to its original level.

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The higher the water is held above its original level the more potential energy that is stored in the water.

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Voltage is the difference between the 2 points. Voltage is sometimes referred to as the potential difference.

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The battery serves as the pump. The push comes from the negative end (pole).

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A voltmeter is used to measure the voltage in a circuit.

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All materials exhibit some resistance to the flow of its electrons. This property is called resistance (R) and is measured in ohms ( ) Materials with little resistance are conductors (metals) Materials that prevent the flow of electrons are insulators (glass, plastics, ceramics, nonmetals)

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What is the name for the flow of electrons in an electric circuit? Current

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In what unit is electrical current measured? Amperes

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What is the basic unit of resistance? The Ohm

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What do we call materials that offer little resistance to the flow of electrons? Conductors

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What instrument is used to measure the flow of current in an electrical circuit? Ammeter

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What term is used to describe opposition to current flow in ordinary conductors such as wires? Resistance

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Give an example of a material that is a good electrical insulator. Glass/ plastic/ non-metals

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What instrument is used to measure Electromotive Force (EMF) between two points such as the poles of a battery? Voltmeter

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George Ohm discovered the relationship between voltage, current and resistance in a circuit. Ohm’s Law The more resistance in a material, then the less current will flow in response to the voltage. IR V This diagram can help you Remember Ohm’s Law.

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What formula is used to calculate current in a circuit? Current (I) = Voltage (E) / Resistance (R)

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What is the resistance of a circuit when a current of 2 amperes flows through a resistor connected to 50 volts? 25 ohms

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What is the current flow in a circuit with an applied voltage of 110 volts and a resistance of 75 ohms? 1.5 amps

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What is the voltage across the resistor if a current of 1 amp flows through a 5 ohm resistor? 5 volts

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The rate at which electrical energy is used is called power. Power = current x voltage The unit for power is the watt.

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What is the formula used to calculate electrical power in a DC circuit? Power (P) = voltage(E) multiplied by current(I)

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How much power is being used in a circuit when the applied voltage is 13.8 volts DC and the current is 10 amperes? 138 watts

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How much power is being used in a circuit when the applied voltage is 12 volts DC and the current is 2.5 amperes? 30 watts

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How many amperes are flowing in a circuit when the applied voltage is 12 volts DC and the load is 120 watts? 10 amperes

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Sometimes it is necessary to convert from small units to larger units or larger units to smaller units. This is when an understanding of the metric prefixes comes in handy.

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12 milliamps = ___ amps 24,000 watts = ___ kilowatts 70 millivolts = ___ centivolts

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15 volts = ___ millivolts ___ microvolts ___ kilovolts ___ megavolts

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Which of the following is equivalent to 500 milliwatts? A. 0.02 watts B. 0.5 watts C. 5 watts D. 50 watts

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How many volts are equal to one kilovolt? One thousand volts

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How many milliamperes is 1.5 amperes? 1500 millamperes

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How many volts are equal to one microvolt? 1 millionth of a volt

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If an ammeter calibrated in amperes is used to measure a 3000-milliampere current, what reading would it show? A. 0.003 amperes B. 0.3 amperes C. 3 amperes D. 3,000,000 amperes

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