Current Flashcards
What is electric current?
Denoted by (I) and measured in amps (A), it is a flow of electrons.
What are the two types of current?
- Direct current (d.c.)
- Alternating current (a.c.)
What is direct current?
d.c. is the type of current that flows from cells and batteries. It can flow in one direction only.
What is alternating current?
a.c. is the type of current supplied by mains electricity. It alternates one way then another as it is produced. In the case of mains, it changes direction every 1/100 of a second. It has a frequency of 50Hz.
What are the two types of circuits?
- Seires circuit
- Parallel circuit
What is a series circuit?
A circuit in which components are connected one after the other. The current will always be the same in a series circuit.
What is a parallel circuit?
A circuit on which components are connected through parallel branches. The current splits in the individual branches.
The total current entering a junction of paths…
…will be equal to the total current exiting the junction of paths.
How is current measured?
With an ammeter placed in series.
What are the effects of current?
- Magnetic effect
- Chemical effect
- Heating effect
What is the magnetic effect?
The movement of charged particles in the wire disrupts a magnetic field.
What is the chemical effect?
This can be seen when two ends of a circuit are placed in an electrolyte solution. Gas bubbles are produced as chemical reactions take place.
What is the heating effect?
Current produces heat. This can be seen in kettles and devices heating up after a long use. This is probably the most important effect in relation to the practical use of electricity.
What can happen due to the heating effect?
- Energy can be lost in electrical transmission through heat loss
- Electrical circuits have to be designed and monitored to avoid fire or melting due to overheating
- Current can be used to heat objects
- Light can be emitted from objects that are heated
State Joule’s law.
The rate of heat produced in a constant resistance conductor is proportional to the square of the current.
How would you demonstrate the magnetic effect?
Set up a circuit with a power source and switch, place a compass over the wire, watch the needle deflect as the circuit is turned on and off.
How would you demonstrate the chemical effect?
Set up a circuit with a power source, rheostat, switch and copper and iron plates in a copper sulphate electrolyte solution, the solution will bubble when the circuit is on.
How would you demonstrate the heating effect?
Set up a circuit with a power source, switch, rheostat, heating coil, calorimeter and thermometer, the temperature will rise proportionally to the square of the current applied.
What is the chemical effect of current also known as?
Electroplating
What can electroplating/electrodisposition be used for?
- Protection
- Aesthetics
- Circuit building
What are the materials we look at the effects of current and voltage for?
- Metallic conductor
- Filament bulb
- Semiconductor (thermistor)
- Electrolyte solution
- Vacuum
- Gas
What is the effect of current and voltage on a metallic conductor?
A metallic conductor obeys Ohm’s law. Voltage is directly proportional to current at constant temperature.
What is the effect of current and voltage on a filament bulb?
The filament bulb gets hotter as current flows. This increases resistance and the current tends to drop off slightly as voltage is increased.
What is the effect of current and voltage on a semiconductor (thermistor)?
When voltage is applied current increases and the semiconductor heats up.
What is the effect of current and voltage on an electrolyte solution with active electrodes?
Obeys Ohm’s law, current is directly proportional to voltage. Straight line through the origin.
What is the effect of current and voltage on an electrolye solution with inactive electrodes?
Behave as a cell with an emf across the electrodes. Until the applied voltage exceeds this emf, no current flows. Directly proportional, straight line but not through the origin.
What is the effect of current and voltage on a vacuum?
Current stars off increasing with voltage, but evens out and constant current flows. (Thermionic emission)
What is the effect of current and voltage on gas?
Current starts off increasing with voltage, evens out but after a while will start increasing again.
