Current Electricity (ii) Flashcards
Voltage
The amount of energy per Coulomb. 1 volt equals 1 Joule per Coulomb.
Current
The rate of flow of charge. 1 amp is equal to 1 coulomb per second. The charge carriers are delocalised electrons in wires.
Voltmeters measure
Energy in a circuit
Potential difference is
Voltage
Ohms law
Current is directly proportional to voltage, provided that other physical properties (like temperature) remain constant
Ohms law equation
Voltage = current x resistance
Volts (V) = Amps (A) x ohms (ohms sign)
V = I x R
Describe how current varies with voltage
As voltage increases so does the current
I-V graphs for a resistor
- resistance = 1/gradient
- current and resistance are inversely proportional
- resistance restricts the flow of current
- low R = high I
- high R = low I
Learn the symbols of a circuit
Workbook
Diodes allow
Current to flow in one direction
Diodes facing the direction of the current is called
Forward bias (current always flows from +ve to -ve)
Diode facing the opposite of direction of current flow is called
Reverse bias and current will not flow
LED
Light emitting diode that will light up when current flows through it at forward bias as long as the voltage is above 0.6V. It will not light up when current flows through it at reverse bias .
LDR
Light dependent resistor
As light intensity increases resistance decreases
Thermistor
As temperature increase resistance decreases
How does current vary with voltage in forward bias
Current increases more rapidly than voltage
Describe how current varies with voltage in reverse bias
The more the voltage increase, the current still remains at 0. If more voltage is used, the current would still be at 0 but would eventually break
What is a diodes purpose
Allows current to flow in one direction
How does the length of a wire effect its resistance
- The longer the wire the higher the resistance (directly proportional)
- sources of error: crocodile clips resisted themselves, the wire was not completely flat therefore the length of the readings would be smaller and imprecise, dont know where to take the readings from as the clips are so thick so dont know where electrical contact is made
Name an advantage and disadvantage of a parallel circuit compared to a series circuit
Adv: individual control of each appliance, if one appliance breaks the rest dont
Disadv: if little appliances need to all work at the same time in parallel, the power supply would overheat and become a fire hazard
Energy transferred=
Current x voltage x time
Rule for current in a series circuit
Current remains constant throughout a series circuit
Rule for voltage in a series circuit
Voltage of the cell is equal to the sum of potential differences
Rule for current in parallel circuit
Current splits at a junction, however comes out as the same value even if it was split unevenly
Rule for voltage in parallel circuit
The same amount of energy/voltage is ‘used’ per circuit of the parallel circuit
Current equation
I = Q/t Current = charge/ time A = C/t
Voltage equation
V= E/Q Voltage = energy / charge V = J/C
Resistance
Ratio of voltage: current or restricts the flow of current
Merge the equations Q=It and E=VQ
E = ItV Energy = current x time x voltage J = A x s x V
I-V for a diode
- at one point in the graph resistance starts to decrease in order to let the current flow
- reverse bias however, the resistance remains massive and never decreases therefore preventing a large current flow
Answer some circuit questions
In workbook
