Electricity Flashcards
Definition of power?
the rate at which electrical energy is transferred to other forms
Explain how you would use an LDR, a variable resistor and a transistor to make a light switch on when the light level in a room drops.
The variable resistor and LDR are placed in series to create a potential divider circuit. In bright light, the resistance of the LDR is low, and therefore the p.d of the transistor is low so the transistor remains off. But, when the light level decreases, the transistor’s input p.d increases due to the fact that the resistance of the LDR increases. This causes the transistor to turn on, allowing current to flow to the lamp.
How can a circuit containing a transistor be used as a switch?
A circuit containing a transistor can be used as a switch because transistors turn on when their input p.d reaches a certain value and when this happens, the transistor allows current to flow to the rest of the circuit.
Explain how potential dividers can be used to run a component that requires a low p.d from a high p.d source.
potential dividers are two resistors which are placed in series in order to split voltage up based on each resistor’s respective resistance.
Why does adding more resistors in parallel make the total resistance of the circuit decrease?
because it causes an increase in current and as current goes up resistance goes down.
Where is an electric field created?
around any Electrically charged object
What happens to the electric field strength as you get closer to the charged object?
It gets stronger
What type of force does a charged object feel in another’s electric field?
Attraction or repulsion
What is the relationship between opposites and like charges?
Opposites attract, like charges repel
Where does the attraction/repulsion force come from?
due to the electric fields of each object interacting
How does distance affect the force between two charged objects?
Greater distance means weaker force
How can electric fields be shown in diagrams?
by drawing electric field lines
Where do electric field lines go from and to?
Positive to negative and are always drawn at a right angle to the surface of a charged object
What is the relationship between line closeness and field strength?
Closer lines indicate stronger field
Field lines show the direction that a force would act on a ——— charge placed at each point and the ——- charge would feel an opposite force.
positive
negative
What can field lines be used to evaluate?
the path that a charge would take if placed in the field.
What is electric current?
term which describes the electrical charge transferred per unit of time
What is needed for current to flow?
Source of potential difference
How is current measured?
Amperes (A)
Who is the electric current unit named after?
André-Marie Ampère
What are the charge carriers in metals?
Electrons
What is the conventional flow of current?
Positive to negative (old idea, incorrect) actually goes from -ve to +ve
What is a characteristic of a closed series circuit?
Current stays the same
What materials allow easier flow of electric charge?
Conductors