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Resistance and Ohm’s Law Name ____________________________________________ Date _________ Opposition to the flow of charge is known as __________________. ( _________ ( ). Its unit is the ). Electric charges are slowed down by ____________________ with ____________ in the wire. The resistance of a wire depends on three things, the __________________ of which it is made, the ____________ and the _____________ of the wire. The _______________ the wire the less resistance but the ______________ the wire the more resistance. Higher resistance means a _____________ ________________ to the flow of ___________. The _____________ the resistance of a wire, the ________ current for a given voltage. _______________ is a good conductor, _________ is a poor conductor. Expressed as an equation: R= Where is the resistivity of the material. Conductors have the _______________ resistivity and ______________ have the biggest resistivity. Example: Suppose you want to connect your stereo to remote speakers. If each wire must be 20 m long and has a cross sectional area of 3.36 x 10-6 m2, what is the resistance of each wire? (copper = 1.68 x 10-8 m). If the wire was aluminum, what would happen to the wire’s resistance? Also the resistance of a metal ______________ with ___________________. At_____________ temperatures the atoms move around more ______________ and get in the way of flowing electric charges. Materials that have essentially zero resistance at very low temperatures are called ______________________. This means that almost no ______________ is wasted. Superconductors are useful where large ______________ are required such as in ____________________ ___________________ and in motors. Ohm’s law identifies the relationship between ________________, __________________ and __________________. It states that __________________________________________________________________ _____________________________________________________________________________ As an equation Ohm’s Law is: As symbols it is: As units it is: Use the Ohm’s Law in the triangle to find the quantity you want. Cover the letter you want to determine with your finger and the remaining two letters show the formula that you need to use. V I x R What is the resistance of a clothes iron that draws a current of 12A from an outlet at 120 V? If a potential difference of 6 V is across a 25 resistance (load) how much current flows through it? What is the potential difference across a 20 resistance (load) that draws 5.5 A from an outlet? The current in an incandescent lamp is 0.5 A when connected to a 120 V circuit, and 0.2 A when connected to a 10 V source. Does the resistance of the lamp change in these cases? Explain your answer and defend it with numerical values.