Definition of Electric Circuits

### Ampere

One ampere is the amount of current flowing in each of two infinitely-long parallel wires of negligible cross-sectional area separated by a distance of one meter in a vacuum that results in a force of exactly 2*10^-7 N per meter of length of wire.

### Current

Current is defined in terms of the force per unit length between parallel current-carrying conductors.

### Resistance

ratio of potential difference applied across a piece of material to the current through the material

### Placement of Voltmeter

must be placed in parallel to measure potential difference between two points circuit does not to be broken

### Ideal Voltmeter

has infinite resistance so it will not allow any current to flow through it and disrupt circuit

### Potential Divider

resistors in series act as 'potential divider'. they split the potential of the source between them.

###
Light-Dependent Resistor (LDR)

Light Sensor

a photo-conductive cell made of semiconducting material whose resistance decreases as the intensity of the incident light increases

###
Negative Temperature Coefficient (NTC) Thermistor

Temperature Sensor

a sensor made of semiconducting material whose resistance decreases as its temperature increases

###
Strain Gauge

Force Sensor

a long thin metal wire whose resistance increases as it is stretched since it becomes longer and thinner

### Resistance

ratio of potential difference applied across a piece of material to the current through the material

### Ohm's Law

for a conductor at constant temperature, the current flowing through ti is proportional to the potential difference across it

### Ohmic Device

a device that obeys Ohm's law for a wide range of potential differences (a device with constant resistance)