Current, Potential Difference & Resistance Flashcards

All 23 cards in this deck

Where in the atom are protons, neutrons and electrons found?

Protons and neutrons are in the nucleus; electrons orbit the nucleus in shells.

What are the relative charges of a proton, a neutron and an electron?

Proton $+1$, neutron $0$, electron $-1$.

What are the relative masses of a proton, a neutron and an electron?

Proton $1$, neutron $1$, electron about $\frac{1}{1836}$ (negligible).

True or false? Almost all of the mass of an atom is in its nucleus.

True. Protons and neutrons are in the nucleus and electrons have negligible mass.

How is an ammeter connected in a circuit, and what does it measure?

In series with the component; it measures the current in it, in amps (A).

In the circuit symbol for a cell, which line shows the positive terminal?

The longer, thinner line (the short thick line is negative).

How does the circuit symbol for an LED differ from the symbol for a diode?

The LED has two small arrows pointing away from the diode symbol (showing light emitted).

What are the steps to draw a circuit diagram to measure the resistance of a piece of wire?

e.g. 50 cm of resistance wire with a low voltage power supply

1. Power supply (cell/battery) in series with the resistance wire.
2. Ammeter in series with the wire.
3. Voltmeter in parallel across the wire (or use an ohmmeter across the wire instead of both meters).

What is potential difference (voltage)?

The energy transferred per unit charge passed.

What is 1 volt equal to in other units?

$1$ joule per coulomb ($1\ \text{J/C}$).

What is the equation linking energy transferred, charge moved and potential difference?

$E = Q \times V$

energy (J) = charge moved (C) $\times$ potential difference (V).

How is a voltmeter connected to measure the potential difference across a component?

In parallel with the component; it reads the potential difference in volts (V).

What is electric current?

The rate of flow of charge.

In a metal, what is the current a flow of?

Electrons (negatively charged).

What is the equation linking charge, current and time?

$Q = I \times t$

charge (C) = current (A) $\times$ time (s).

What two things must a circuit have for there to be a current in it?

A complete (closed) circuit and a source of potential difference.

What does it mean that current is conserved at a junction?

The total current into a junction equals the total current out of it.

True or false? Current is used up as it passes through a lamp.

False. Current is conserved — the same current leaves the lamp as enters it; energy is transferred, not current.

What is the equation linking potential difference, current and resistance?

$V = I \times R$

potential difference (V) = current (A) $\times$ resistance ($\Omega$).

How is a variable resistor used to control the current in a circuit?

Increasing its resistance increases the total circuit resistance, which reduces (limits) the current.

True or false? Resistance is measured in ohms, and $1\ \Omega$ is $1$ volt per amp.

True. It follows from $R = V \div I$.

What happens to the total potential difference when cells are connected in series, all facing the same way?

The potential differences of the cells add together, e.g. three 1.5 V cells give 4.5 V.

In which direction do electrons actually move around a circuit?

From the negative terminal round to the positive terminal, the opposite way to conventional current.