current electricity & DC circuits (I) Flashcards
what does 1A mean
1A = 1Cs^-1
charge of 1C flowing in the circuit in 1s
one coulomb
quantity of electric charge that flows past a given point in a circuit when a steady current of 1 ampere flows for one second
how many electrons in 1C
6.25x10^18
charge on one electron
1.60x10^-19 C
1 milliamperes (mA)
1x10^-3 A
1 microampere
1x10^-6 A
what is the cause and effect in a circuit
cause: voltage
effect: current
role of battery in the circuit
- give energy to the electrons so that they can flow and be a current
- provides a potential diff
electromotive force (e.m.f)
defined as the energy converted from non-electrical forms to electrical forms when one coulomb of charge passes through the cell
what does 1V mean
e.m.f. of 1V means that it takes 1J of work to bring 1C of charge from the positive end to negative end of a circuit
potential difference (p.d.)
defined as the energy converted from electrical forms to other forms of energy when one coulomb of charge passes from one point to another point
difference between potential, voltage and e.m.f., p.d.
potential & voltage w reference to 1 pt
e.m.f. & p.d. w reference to 2 pts
resistance
ratio of the potential difference V across the conductor to the current I flowing through it
(in terms of motion of electrons)
resistance in the resistor is caused by the collision of free electrons with the vibrating atoms/ions in their path (under an applied potential difference)
state ohm’s law
ohm’s law states that the current flowing in a metallic conductor is directly proportional to the potential difference across its ends, provided the physical conditions are constant
(eg. temperature)
ohmic conductor
obeys ohm’s law
- relation between I and V is linear
- graph is a straight line passing through origin
non-ohmic conductor
does not obey ohm’s law
- relation between I and V is not linear
- graph is not a straight line passing through the origin
thinner wire vs thicker wires (resistance)
thinner wire -> higher resistance than thicker
longer wire vs shorter wire (resistance)
longer wire -> higher resistance than shorter wire
what is meant by a “current of 0.70A”
means that a total charge of 0.70C is flowing through every point in the circuit in 1s
is the bulb an ohmic conductor (no)
no
for ohmic conductor, the current I is proportional to the voltage V. from the graph, the graph gradient is not constant, hence I is not proportional to V, hence the conductor is not ohmic
state one possible source of error in this experiment and explain how its effect can be minimised
- is an ohmic conductor but results show otherwise
- ohm’s law: temp must b constant
the temp of the bulb/wire may change as the reading is being taken
this will result in a variation of the bulb’s resistance
the switch should only be closed when readings are taken
when switch S is open, ammeter reading is 0
e.m.f. 16v
state the value of the potential diff across switch s when it is open/closed
closed: 0V
open: 16V
explain what the value of potential difference across the switch means (0V and 16V when closed and open)
- 0V of electrical energy required to drive 1C of positive charge across the switch since the switch has negligible resistance when the switch is closed
- when the switch is open, 16V is actually measuring the p.d. across the cell
electric current
measure of the rate of flow of electric charge through a given cross-section of a conductor