Circuits Flashcards
A charged atom is called an…?
Ion. This can be made by taking away or adding electrons.
Rubbing a balloon charges it with…?
Static electricity. This charge makes the balloon attract to things.
Rubbing a polythene rod with a dry cloth transfers electrons to the surface atoms of the rod to the cloth so it becomes positively charged.
Rubbing a Perspex rod with a dry cloth transfers electrons from the surface atoms of the cloth to the rod so the cloth becomes negatively charged.
Learn electric circuit symbols.
Yes.
Current is a measure of…?
Rate of flow of charge
When a toe his switched on, millions of electrons pass through the bulb every second carrying a negative charge. Metals contain lots of electrons that move freely around them to hold positively and negatively charged particles together.
Yes.
Electric charge is measured in coulombs.
A current if one amp is a rate of flow of charge of one coulomb per second.
Yes.
Current (amps) = charge flow in coulombs/time taken in seconds
I = Q/T
Ammeters are connected I series and measures the current through components.
Voltage is measured in parallel with the bulb so it measures the potential difference across it.
Potential different = work done in joules/charge in coulombs
V = W/Q
Voltage = current x resistance
V = IR
If the current is directly proportional to the potential difference for a wire at constant temperature we say the component obeys…?
Ohm’s Law
Why is a wire an ohmic conductor?
Because its resistance is constant and reversing the potential difference makes no difference to the line on a current-potential difference graph.
In a filament bulb…
- It is not an ohmic conductor
- The line curves away from the current axis
- The resistance of the metal filament increases as its temperature increases because ions in the metal filament vibrate more as the temperature increases so they resist the passage of electrons through the bulb
- Resistance is always the same no matter which way the flow of charge
In a diode…
- In the forward direction, the line curves towards the current axis so the current is not directly proportional to the potential difference and a diode is not an ohmic conductor
- There is no current in the reverse direction so resistance in the reverse is much higher than in the forward direction
In a thermistor…
If temperature is increased, resistance decreases
In an LDR…
Resistance decreases when the light intensity on it increases
In a series circuit…
- The same current passed through all components in series with each other
- The voltage is shared between components
- Provided cells act in the same direction, the total potential difference if the cells is the sum if the potential difference of each cell
- The total resistance of components is equal to the sum of the resistance of each component
In a parallel circuit…
- The total current is the sum of the current through each component
- The potential difference across each component is the same because each electron will only pass through one component or the other
Why is a cell necessary?
To push electrons around a complete circuit
Why is a switch necessary?
To turn the current on or off.
A bulb will emit light when current passes through it.
Yes.
A diode allows light through in one direction only.
Yes.
What does an LED do?
Emits light when current passes through it
