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Transcript
Grade 9 Academic Science – Unit 4 Electricity Laboratory - Relationship between Current and Potential Difference Section 13.8 Page 567 Stuff we know…. All materials are made up from atoms, AND all atoms consist of subatomic particles: protons, neutrons and electrons. Protons have a positive electrical charge, neutrons have no electrical charge while electrons have a negative electrical charge. Atoms are held together by powerful forces of attraction existing between the atoms nucleus and the electrons in its outer shell. If we separate the electrons from the nucleus, the electrons exert a potential of attraction called a POTENTIAL DIFFERENCE (…wow…now I get that one…) The basic electrical circuit consists of three separate but very much related quantities: Voltage (V), Current (I) and Resistance (Ω). If we create a circuit for the electrons to move back to the attraction of the protons (RECALL: Law of Electric Charges whereby opposite charges attract), the flow of electrons is called a CURRENT. Current is the movement or flow of electrical charge, and current is measured in amperes or amps (A). Electrons typically flow from the negative to the positive in a circuit (see diagram). An amp is the number of electrons passing a certain point in the circuit in one second. NOTE: Current can be expressed in milli-amps (mA = 10-3A). Current that flows in a single direction is called Direct Current (DC) and current that alternates back and forth through the circuit is known as Alternating Current (AC). If the electrons do not flow freely through the circuit, the restriction to this flow is called RESISTANCE. VOLTAGE is like the force that pushes electrons. If voltage is increased, it has a greater ability to "push" the electrons through a given circuit. the greater the voltage, the greater is the pressure (or pushing force) and the greater is the capacity to do work. The difference in voltage between any two spots in a circuit is known as the Voltage Drop. Relationship between Voltage and Current in a Circuit of Constant Resistance The illustration shows an electrical circuit. The Voltmeter is connected in a parallel circuit to the load (i.e., circuit resistance (R)). This connection is called “across the load” and it is measuring the drop in voltage across the load (i.e., How much energy is used up to run the resistor). The Ammeter is connected in series with the circuit. It is measuring the current the line The graph shows the linear relationship between Voltage (V) and Current (I). NOTE: The graph would be very different if resistance changed. IN YOUR OWN WORDS, describe the relationship between the two factors. In other words, how does voltage change as current changes? …and visa versa, how does flow (i.e., current change when there is a change in push (i.e., voltage)? in From our houses, we know that some machines (e.g., stoves and clothes dryers) require more potential difference that some other machines (e.g., night lights, battery rechargers). What effect does a higher potential have on current flowing through the wires of each machine? Purpose To determine the relationship between the current and the potential difference What is your hypothesis? In other words, what do you predict will happen in the experiment? Materials Alligator clip wires Voltmeter Ammeter Power supply Circuit (light) board One light (resistor or load) Graph Paper Switch (optional) Methods Construct a table to record your observations. Make it logical and practical. Make sure you collect sufficient data to answer your question(s). Draw a circuit diagrams to connect the light to the power supply, AND properly connects the ammeter in series to the circuit and the voltmeter in parallel to the load Build the circuit using with one light, a voltmeter and an ammeter Turn on the power supply to a LOW SETTING Record the amps and the volts in your data table INCREASE the power setting to 25% maximum Record the amps and the volts in your data table INCREASE the power setting to 50% maximum Record the amps and the volts in your data table INCREASE the power setting to 75% maximum Record the amps and the volts in your data table INCREASE the power setting to 100% maximum Record the amps and the volts in your data table On graph paper, plot the relationship between potential difference and current. HINT: Put potential difference on the y-axis and current on the x-axis. Looking at the date, draw a LINE OF BEST FIT. Calculate the slope of the line. The formula is SLOPE = RISE / RUN Answer Questions 6(e) and 6(g) on Page 567 of your textbook.