Produces constant voltage to make charges move (current)
- Electrons free to move in conductors → carry energy through circuit.
- Energy comes from a battery (converts chemical → electrical energy)
- As energy is transformed, a potential difference V develops across the battery’s terminals (called EMF).
amount of charge that passes through an area in a given amount of time
units: Amps → (1A = C/s)
Equations for current (I)
Current in a metal wire is proprotional to what?
Current (I) proportional to potential diff (V) applied to its 2 ends
plates/rods (made of dissimilar metals)
solution (ie a dilute acid)
part of electrode outside of solution (where you connect wires/circuits)
What is the simplest BATTERY made of?
2 electrodes (+ and –) & 1 electrolyte
continuous conducting path connected between terminals of a battery
continuous conducting path
break in circuit (ie. cut wire)
common conductor (provides continuity)
current direction in a circuit = direction + charge would flow
opposition to flow of charge
units: ohms → (1 Ω = 1 V/A)
In a device that produces heat (ie. toaster) what kind of resistance do you want?
HIGH resistance needed (otherwise no heat produced)
Do you want low/high resistance in wires?
LOW resistance wires (to minimize energy loss)
Resistance of a uniform wire EQUATION
p = constant of proportionality (RESISITIVITY) → units (Ω m) → depends on material used
What is special about silver?
It has the lowest resistivity (p), therefore lowest resistance (R) making it best conductor → electrons free to move
Ohm’s Law EQUATION
V = IR
To what materials can Ohm’s law be applied?
Ohmic materials: metal conductors (R is constant) whose temperature doesn’t change much
What are resistors used for?
used to control (reduce) the amount of current in a circuit
What factors does resistance depend on?
type of material wire made of, length, cross sectional area
amount of current a material can carry
(reciprocal of resistivity)
Electrical conductivity EQUATION
How does temperature effect resistance?
R of metals INCREASES at higher temp
(because atoms move faster and interfere more with flow of electrons)
amount work down / time
rate energy is transformed
P = IV
P = W/t
Do thicker wires have less or more resistance?
switches that open the circuit when current exceeds a safe value to prevent overloading
no longer a complete conducting path (no current can flow)
as if R = infinity
two wires touched that shouldn’t have
Q: Why shouldn’t properly rated fuses be replaced by higher-rated ones?
Fuse won’t blow as intended and high current will harm (ie. melt) whole circuit…
Direct Current (DC)
one-directional flow of electric charge
reverse direction many times/sec (sinusoidal)
AC → DC current
DC → AC