Current Electricty II Flashcards
current =
rate of flow of charge
current (units) =
Amps (A)
Charge (coulombs) =
current (A) x time (s)
voltage =
energy per unit charge
voltage (units) =
Volts (V)
1 joule per coulomb =
1 volt
voltage (V) =
current (A) x resistance (Ω)
energy (J) =
current (A) x time (s) x voltage (V)
Current in a metallic conductor =
flow of negatively charged electrons
LED can be used to indicate …
the presence of a circuit
Describe how current varies in resistors, wires, filament bulbs and diodes.
- If you increase the resistance the current will decrease.
- Resistors, wires, filament bulbs and diodes all create resistance in a circuit and so the current will decrease
- This can be investigated using an ammeter and measuring the current with and without these components, or with different voltage levels (measured by voltage)
Increasing the resistance will ….
decrease the current
Decreasing the resistance will ,,,
increase the current
Describe how illumination affects the resistance of an LDR and how temperature affects the resistance of a thermistor.
- An LDR is a light dependent resistor. Its resistance changes with the intensity of light. The brighter the light is, the less resistance; the less light MORE resistance
- Thermistors are temperature dependent resistors. In hot conditions, there will be less resistance, whereas in cold, the resistance is greater
Resistance at constant temperature :
current flowing through the resistor at a constant temperature is directly proportional to the potential difference across it. A constant that gives a graph like this is said to follow Ohm’s law
The filament lamp : Resistance
- Common type of light bulb
- Contains a thin wire called filament. This heats up when the electric current passes through it and produces light
- It doesn’t follow Ohm’s law
- Its resistance increases as the temperatures of its filament increases
The Diode : Resistance
- Diodes are electronic components that can be used to regulate the p.d. In circuits and make logic gates
- LEDs give off lights and are often used for indicator lights in electrical equipment
- Has a very high resistance in one direction ; current can only flow in the other direction
Design a circuit and experiment to investigate Current (I) – Voltage (V) characteristics.
- Turn power supply up until the p.d. across the lamp is 12V
- Record p.d. and current
- Calculate resistance V = IR
- Change voltage to see relationship
