Current, Potential Difference & Resistance Flashcards
All 22 cards in this deck
Where in an atom are protons and neutrons found?
In the nucleus at the centre of the atom (electrons orbit around it in shells).
What are the relative charges of a proton, a neutron and an electron?
Proton +1, neutron 0, electron −1.
True or false? An atom has equal numbers of protons and electrons, so it has no overall charge.
True. The + charge of the protons cancels the − charge of the electrons.
On the circuit symbol for a cell, which line is the positive terminal?
The longer, thinner line (the short thick line is the negative terminal).
How does the circuit symbol for a battery differ from the symbol for a single cell?
A battery shows two or more cell symbols joined in a line (two or more long/short line pairs).
How is the circuit symbol for a variable resistor drawn?
A rectangle (resistor) with a diagonal arrow drawn through it.
True or false? The circuit symbol for a thermistor is a triangle pointing at a straight line.
False. That is the symbol for a diode; a thermistor is a rectangle with a diagonal line through it that has a short flat end.
How is the circuit symbol for an LED different from the symbol for an ordinary diode?
The LED has two small arrows pointing away from the diode symbol (light coming out).
What is potential difference (voltage)?
The energy transferred per unit charge passed; measured in volts (V).
What is 1 volt equal to in terms of joules and coulombs?
1 volt = 1 joule per coulomb (1 V = 1 J/C).
How should a voltmeter be connected to measure the potential difference across a component?
In parallel with the component (across it).
What is the equation linking energy transferred, charge and potential difference?
energy transferred (J) = charge moved (C) × potential difference (V), .
What is electric current?
The rate of flow of charge; measured in amps (A).
True or false? The current in a metal wire is a flow of protons.
False. In metals the current is a flow of electrons.
How should an ammeter be connected to measure the current in a component?
In series with the component.
What is the equation linking charge, current and time?
charge (C) = current (A) × time (s), .
What two things must a circuit have for there to be a current in it?
It must be a closed (complete) circuit and include a source of potential difference.
What does it mean to say current is conserved at a junction?
The total current flowing into the junction equals the total current flowing out of it.
State the equation linking potential difference, current and resistance, with units.
potential difference (V) = current (A) × resistance (Ω), V = I × R.
True or false? Increasing the resistance in a circuit increases the current.
False. For a fixed potential difference, increasing the resistance decreases the current.
How is the circuit symbol for a filament lamp drawn?
A circle with a cross (X) drawn inside it.
In circuit diagrams current is drawn flowing from + to −. Which way do the electrons actually flow?
From the negative terminal to the positive terminal (the opposite way).