Chapter 20 Flashcards
(23 cards)
Electric current flows in what direction?
Positive
Drift speed
Speed of electrons move in a wire
Suppose a current-carrying wire has a cross-sectional area that gradually becomes smaller along the wire so that the wire is like a very long, truncated cone. How does the drift speed vary along the wire?
It speeds up as the cross section becomes smaller.
Ammeter
Measure current in series
Voltmeter
Measures voltage in parallel
Multimeter
Device measuring both current and voltage
Ohm’s Law
The potential difference (V) creates an electric field that produces a current (I)
Ohm’s Law
Resistance is constant
Ohmic
Resistor obey Ohm’s Law
Nonohmic
Resistor DOES NOT obey Ohm’s Law
Resistivity
The amount of collisions electrons undergo as they move through a conductor. Different for different materials
Suppose an electrical wire is replaced with one having every linear dimension doubled (i.e., the length and radius have twice their original values). The wire now has?
Less resistance
If this wire is melted down and recast into one with twice the length, what is the new resistance as a multiple of the original?
The same
Electrical Energy and Power
When charge flows through a resistor, it loses some electrical potential energy to increasing the internal energy of the resistor. By the time the charge returns, some chemical energy from the battery has been transferred to thermal energy, increasing the temperature of the resistor
How does temperature effect resistance?
Electrons move faster. Higher temperature, higher resistance
Resistors, A and B, are connected in a series circuit with a battery. The resistance of A is twice that of B. Which resistor dissipates more power?
Resistor A
The diameter of wire A is greater than the diameter of wire B, but their lengths and resistivity’s are identical. For a given voltage difference across the ends, what is the relationship between PA and PB, the dissipated power for wires A and B, respectively>
PA> PB; bigger wire, more power
Household circuits
DEVICES in the house are in PARALLEL
One wire is connected to ground, and the other “hot” wire, is at a potential of 120 V
A METER AND CIRCUIT BREAKER (or a fuse) are connected in SERIES
5 mA
Shock sensation, no damage
> 10 mA
Difficult to let go
100 mA
Fatal
Case ground (third wire)
Protect from short
GFI
Cuts leaking currents
