Grade 9 Science: Ohm's Law & Safety PDF

🡽 11.3 Ohm’s Law & Short Circuits Grade 9 Science, Academic Reference: Pearson Investigating Science 9 – section 11.3  Learning Goals To understand Ohm’s Law, which describes the relationship between potential difference, current and resistance. To be able to identify a...

🡽 11.3 Ohm’s Law & Short Circuits Grade 9 Science, Academic Reference: Pearson Investigating Science 9 – section 11.3  Learning Goals To understand Ohm’s Law, which describes the relationship between potential difference, current and resistance. To be able to identify a short circuit and the safety devices used in electrical circuits.  Potential Difference, Current and Resistance Ohm’s Law describes the relationship between voltage (V), resistance (R) and current (I) in electric circuits. This can be represented mathematically V = I x R  Ohm’s Law Ohm’s law states that, as long as temperature stays the same: The resistance of a conductor remains constant. The current is directly proportional to the voltage. ( if one increases, the other must increase)  Ohm’s Law Visual Representation of Ohm’s Law http://phet.colorado.edu/en/simulation/ohms-law  Potential Difference, Current and Resistance If two of the variables are known, the third can be calculated. The formula can be arranged in other ways: V=IxR I = V/R R = V/I  Example Problem 1 Example: An electric toaster is connected to a 120 V outlet. If the heating element in the toaster has a resistance of 14 Ω, calculate the current flowing through it. (Use GRESS) Given V= 120 V, R =14Ω Required I= ? A Equation I= V/R Solve I= 120 V / 14 Ω I= 8.57 A Statement The current in the toaster is 8.57 A. II. Purpose of Resistors All conductors resist the flow of electrons to some extent. Resistors slow the current; can prevent fires Resistance Temperature affects resistance. As temperature increases, resistance increases and conductivity decreases. As temperature decreases, resistance decreases and conductivity increases. III. Short Circuits short circuit is an accidental low-resistance connection between two points in a circuit, often causing excess current flow. Short Circuit Current can flow more easily through the wire path than through the light bulbs dangerous fuses and circuit breakers prevents short circuits Need help with V, I, R? Check this out: https://www.youtube.com/watch?v=J4Vq-xHqUo8 IV. Safety and Electricity a. Fuses ○ disposable items ○ melt when current is too high ○ opens circuits on purpose to shut it down b. Circuit Breakers found in houses and buildings reusable can be reset when “fuse is blown’’ (when you use the toaster, the kettle AND the stove at the same time, for example) c. Three Pronged Plug has a grounding pin sends extra current to the ground d. GFCI Ground Fault Circuit Interrupter used near water sources opens current when water gets in the outlet must be in kitchens, bathrooms etc. Practice Makes It Permanent! Pg. 460-461, check answers in back of textbook Pg 467 #1-12 Text online: sciencesource.ca Login: jcr Pw: jcraccess Don’t forget about the upcoming unit test!