Electric Currents

Question 1

Electric Potential Difference

Answer 1

*
(ΔV)
Electric potential energy difference per unit charge between two points in an electric field
(ΔV=ΔEe/q OR ΔV=W/q)

Question 2

Resistance

Answer 2

*
(R)
Ratio of potential difference applied to a device to the current through the device
(R=V/I)

Question 2

Electronvolt

Answer 2

*
(eV)
Energy gained by an electron moving through an electric potential difference of one volt

Work done moving an electron through an electric potential difference of one volt
(1eV=1.6X10^-19 J)

Question 3

Resistor

Answer 3

Device with a constant resistance (Ohmic device) over a wide range of potential differences

Question 3

Electric Current

Answer 3

*
(I)
Current is defined in terms of the force per unit length between parallel current-carrying conductors
NOTE one ampere of current is the amount of current in each of two infinitely long straight wires one meter apart experiencing a magnetic force per unit length of 2X10^-7 newtons

Question 4

Ohms Law

Answer 4

*
Current flowing thorugh a device is proportional to the potential difference applied across it providing the temp is constant
Note R=V/I is not a statement of Ohm’s Law

Question 5

Ohmic Device

Answer 5

One whose resistance remains constant over a wide range of potential differences (ex, resistor)

Question 5

Non-Ohmic Device

Answer 5

One whose resistance does not remain constant over a wide range of potential differences (ex, filament lamp)

Question 5

Electromotive Force

Answer 5

*
(emf) (ε)
Total energy difference per unit charge around a circuit (total energy per unit charge made available by the chemical reaction in the battery
ε=ΔEe/q OR ε=W/q

Question 6

Internal Resistance

Answer 6

(r)
Resistance inside a battery that causes the battery’s terminal potential difference to be less than its emf
Note internal resistance in a meter causes it not to act as an ideal meter

Question 7

Ideal Ammeter

Answer 7

One with zero internal resistance (placed in series)

Question 7

Ideal Voltmeter

Answer 7

One with infinite internal resistance (placed in parallel)

Question 8

Potential Divider

Answer 8

two resistors placed in series that divide up the battery’s potential difference
R1/R2=V1/V2

Question 8

Negative Temperature Coefficient (NTC) Thermistor

Answer 8

sensor whose resistance depends on its temp, increase in temp causes decrease in resistance

Question 8

Light-Dependent Resistor

Answer 8

(LDR)
Sensor whose resistance depends on amount of light shining on its surface- increase in light causes a decrease in resistance

Question 9

Strain Gauge

Answer 9

Sensor whose output voltage depends on any small extension or compression that occurs which results in a change of length