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# Electric Current Calculations P

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A set of slides created to teach Electric Current Calculations to grade 10 pupils following the NSC Caps syllabus in Cape Town.

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### Transcript of "Electric Current Calculations P"

1. 1. Electric Current Calculations K Warne V1 R1 A VT V2 R2 A1 A2
2. 2. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Electrical Circuits A V1 Voltmeter Ammeter Resistance The Ammeter measures the current flowing in the circuit. (Amps A) The Voltmeter Measures potential difference or voltage in volts. (V) The Resistance of the Resistor is given in Ohms (Ω). V1 = V2 V2
3. 3. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Series Circuits • Adding resistors in series…increases the total resistance - because all the current flows through all the resistors. Rt = R1 + R2 • The total potential difference (voltage) is the sum of the potential differences of the resistors – the total potential loss must equal the all the potential lost along the way. Vt = V1 + V2 The potential differences will be proportional to the resistances. • The current flowing is the same all over the circuit and would decrease as more resistances are added - I = I2 = I3 VTA V1 V2 R1 R2 VT V1 v2 A VT A2 A3 3Ω1Ω 12v VT = 12 V V1 = 3 V V2 = 9 V I = ...
4. 4. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Parallel Circuits • Adding resistors in parallel…decreases the total resistance. 1 1 1 Rt R1 R2 • The potential difference (voltage) is EQUAL over the resistances – there is no potential lost between the resistors and the cells. VT = V1 = V2 • The current flowing is divided between the resistances and would increase as more resistances are added- more routes for the current to flow. = + V1 R1 A VT V2 R2 A1 A2 IT= I1 + I2
5. 5. Electric Current in a Conductor  Conventional current - positive to negative  Maintaining a current  Conductor - closed circuit  Potential difference  Replacement of charges - SOURCE + - + - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + e- e- e- e-e- e- e- e-e- e- e- e-e- e- e- e-e- e-e- e-e-+ - e- e- e- <------- electrons “Positive spaces” ------> Conventional current is the movement of positive “spaces” from + to - in a conductor. Conventional current e- If 160 C of charge flow through the ammeter in 3s what current is flowing? The current is the number of charges passing any point in one second Current (I) = Charge(Q) Time (t)
6. 6. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Calculating Current Calculate the current flowing through the circuit. + _ Ammeter A53.3333 If 160 C of charge flow through the ammeter in 3 s what current is flowing? I = Q/t = 160/3 =53.3 A
7. 7. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net Current & Resistance RESISTANCE • Electrical charge experiences resistance as it moves through a conductor. • The resistance is due to collisions with particles in the metal atoms and ions. • The moving charges lose kinetic energy in the collisions which heat up the conductor. +_ CURRENT: An electrical current is a movement of charges through a conducting material from positive to negative. (?!)
8. 8. Effects of Current +_ Electric current generates heat in a conductor. +_ A small current (0.1A) would have only a few charges flowing. A large current (15A) would have a large number of charges flowing and generate far more heat. As a conductor heats up the RESISTANCE INCREASES.
9. 9. Factors affecting Resistance Material: Different materials have different resistance. Length: Increasing the length will increase the resistance. Temperature: As temp increases – atoms vibrate faster RESISTANCE INCREASES. + - + - A V 1. Material 2. Length 3. Temperature R
10. 10. Current, voltage & resistance We define the unit of resistance; one ohm () is one volt per ampere. R = V/I 1 = 1V/1A + - + - A V The ratio: Voltage Current will always give a constant value for any resistor. If the resistance increases the ratio increases. We therefore use this ratio to represent the resistance of a resistor. R Resistance (R) =Voltage (V) Current (I) Ohm’s law: The current passing through a resistor is directly proportional to the potential difference across the resistor provided the temperature remains constant.
11. 11. Hi - This is a SAMPLE presentation only. My FULL presentations, which contain loads more slides (with all the gaps filled in) as well as other resources, are freely available on my resource sharing website: www.warnescience.net (paste into your browser if link above does not work) Have a look and enjoy! Keith Warne
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