Topic 10 - Electricity And Circuits Flashcards
What is current?
The rate of flow of charge (A)
What is a series circuit?
The different components are connected in a line end to end between +ve and -ve of the power supply
What is a parallel circuit?
Each component is separately connected to the +ve and -ve of the supply.
Where are voltmeters connected in a circuit?
Always connected parallel with a component to measure the potential difference across it.
What is potential difference (voltage)?
The energy transferred per unit charge passed and hence that the volt is a joule per coulomb
What is the equation for energy transferred?
Energy transferred(J) = charge moved(coulomb,C) x potential difference (V)
E =Q x V
What does an ammeter do in a circuit?
It’s connected in series with a component to measure the current in the component
What is an electric current?
The rate of flow of charges
What is current in metals?
A flow of electrons
What is the equation for charge?
Charge (C) = current (A) x time (S)
Q = I x t
What happens when a closed circuit includes a source of potential difference?
There will be current in the circuit
Where is current conserved in a circuit?
At a junction in a circuit
What is the equation for potential difference?
Potential difference (v) = current (A) x resistant (Ω)
V = I x R
Why does resistance increase if two resistors are in series circuit?
Both resistors share the total p.d. The p.d across each resistor is lower so current through each resistor is also lower. In series circuit current is same everywhere so total current in circuit is reduced when resistor is added. So total resistance of circuit increases.
Why does the resistance decrease with two resistors in a parallel circuit?
In parallel both resistors have same p.d. TMT pushing force making current flow is same as source p.d for each resistor added. Adding another loop, current has more than one direction to go in which increases total current that can flow around circuit. V=IR an increase in current means decrease in total resistance of circuit.
What happens when there’s an electric current in a resistor?
There is an energy transfer which heats the resistor.
What happens when an electrical current does work against electrical resistance?
Electrical energy is dissipated as thermal energy in the surroundings.
Why is there an energy transfer when there is an electric current in a resistor?
Because of the result of collisions between electrons and the ions in the lattice
What is the equation for energy transferred?
Energy transferred (J) = current (A) x potential difference (v) x time (s) E = I x V x t
What is power?
The energy transferred per second measured in watts.
What is the equation for power?
Power (W) = energy transferred (J) / time taken (S)
P = E / t
What is direct current (d.c)?
Movement of charge in one direction only (cells + batteries supply d.c)
What is alternating current (a.c)?
The movement of charge that changes direction
What is the equation for electrical power with P.D?
Electrical power (w) = current (a) x potential difference (v) P = I x V
What is the equation for electrical power with resistance?
electrical power (W) = current squared (a2) x resistance (Ω) P = I^2 x R
What is the UK domestic supply of a.c + voltage?
a.c at a frequency of 50Hz + voltage of 230 V
How is an alternating current produced?
They’re produced by alternating voltages (positive + negative ends of p.d keep alternating)
How is direct current produced?
Created by direct voltage (a p.d that is only positive or negative)
What’s the difference between direct + alternating current?
In d.c charges always move in same direction but in a.c charges are constantly changing direction.
What is the live wire?
Brown wire. Carries voltage, alternates between +ve & -ve voltage of 230V.
What is the neutral wire?
Blue wire. Completes the circuit, electricity flows in through live wire + out through neutral wire. 0V
What is the earth wire?
Green + yellow. It’s for safety + protecting the wiring. Carries the current sway is something goes wrong + stops appliance casing becoming live. At 0V.
What are circuit breakers?
They prevent electrical overloads turning off when there is a large current. They turn off quicker than time for fuse to melt. Can be reset but more expensive than fuse.
Advantages of the heating effect of an electric current
Good use in room heaters + water heating coils where electricity converted into heat energy.
Electric bulb glows when heated, thus gives out light.
Describe the disadvantages of the heating effect of an electric current
Wastage of energy in overhead cables
Cooling systems + heat sinks need to be added to circuits -> more cost.
Explain the design and construction of series circuits for testing and measuring
Components are connected in a line end to end between +ive & -ive of the power supply.
Voltmeters are connected parallel to filament lamp.
Current is the same everywhere. Total P.d is shared between components.
How do fuses prevent electrical overloads?
If the amount of current is greater than the fuse rating it melts + breaks the circuit + cuts off live supply. Prevents fire + shock.
What happens if you change the resistance in a series circuit?
Increasing number of lamps will decrease current because lamps resist current.
How does a variable resistor change the resistance in a circuit?
As I = V / R, Increasing the total resistance by increasing the variable resistor’s resistance lowers the current through the circuit
What is charge?
The charged particles that move around a circuit
What is potential difference?
The energy transferred per unit charge
How do low resistance wires reduce unwanted energy transfer?
Less energy will be wasted as less collisions occur with the lattice structure so less thermal energy dissipated to surroundings.
Explain why switches and fuses should be connected in the live wire of a domestic circuit
So the socket/appliance isn’t live when it is switched off.
