Published on April 21, 2013
Grade 12 Electric Current - + N S Force N X S Keith Warne SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
Current Carrying Conductors Current in same direction. Two parallel current carrying conductors with current flowing in the same direction attract each other by the reduced magnetic flux density between the conductors. SAMPLE ONLY X Magnetic flux cancels out Conductors attract! SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
Current and Charge The Ampere: The current in two parallel conductors, of infinite length, one meter apart, in a vacuum which will produce a force of 2 x 10 -7 N per meter of length. 1A 2x10-7N 1 meter 1A The Coulomb: Quantity of charge passing any cross section of a conductor in one second when a current of 1A is flowing. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
Ohm’s Law - Practical AIM: – Investigate the relationship between the potential difference across a resistor and the current flowing through it. rheostat – Determine the resistance of a resistor. METHOD: 1. Set up the circuit as shown. A 2. Using the rheostat to vary the current in the circuit, obtain a range of readings for the potential difference across R for different currents. SAMPLE ONLY SAMPLE ONLY V Resistance R SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
Ohm’s Law - Results Analysis Results V (V) 3.40 3.50 3.70 3.90 4.20 4.40 Voltage (V) I (A) 0.80 0.81 0.85 0.90 0.95 Current vs Voltage 4.20 4.00 3.80 3.60 3.40 3.20 3.00 0.75 0.80 0.85 0.90 Current (A) 0.95 The graph is a straight line showing that the current (I) is directly proportional to the voltage (V). SAMPLE ONLY SAMPLE ONLY 1.00 SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
EMF - LOST VOLTS 350V Vex EMF = 400V Internal circuit (50) (Vint =50V) lost due to internal resistance Ri in moving across cell Closed Circuit!! A I = IA (400) Lost Volts Vex= 350v Vex 350V (50) Emf = Vex + “lost volts” = IRex+ IRi =I(Rex + ri ) Resistance R Emf SAMPLE ONLY = Vext +V…… ONLY SAMPLE SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
Series Power • Increasing the resistance in the circuit decreases the current. • Lower current flowing through each bulb results in a lower voltage drop and therefore less power is dissipated. • . (No internal resistance) The voltage drop across the whole circuit remains constant SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
Parallel Bulb Brightness A 10 W bulb has a LOWER resistance than a 6 W bulb and so draws a higher current and delivers more power UNDER THE SAME VOLTAGE. R10w = V/I = 12/0.833 = 14.4 P6 = VI = (12)(0.500) =6W R6w = V/I = 12/0.5 = 24 P10 = VI = (12)(0.833) = 10 W LOWER resistance gives more power inSAMPLE ONLY parallel! SAMPLE ONLY SAMPLE ONLY Since voltages in parallel are equal the bulb with the highest current (lowest R) For FULL presentation click HERE >> www.warnescience.net will have most power.
Electricity Questions 6V 6.1 The battery has an internal resistance of 1. L1 & L2 each have a resistance of 3 . What will the reading on V be when S is closed? (7) 6.2 An electric motor is rated at 2000W; 250V. Fuses rated at 5A, 10A, & 25A are available. 6.2.1 Which fuse would be most suitable to protect the motor? (5) 6.2.2 Calculate the cost of operating the electric motor for 24 hours if one kilowatt-hour of energy costs 34 cents? (3) SAMPLE ONLY SAMPLE ONLY A V L2 X L1 X S SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
WarneScience Hi… This is a SAMPLE presentation only. My FULL presentations, which contain loads more slides and 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! SAMPLE ONLY Keith Warne SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
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