Electrical quantities: voltage, current and resistance

The TV remote works with two batteries printed with $1,5\ \text{V}$. What electrical quantity does this number indicate? Explain in your own words what it tells us about the "push" the battery provides to the charges in the circuit.

Order these batteries from greatest to least "push" on the charges: a smoke detector's $9\ \text{V}$ battery, an old torch's $4,5\ \text{V}$ battery, and a wall clock's $1,5\ \text{V}$ battery. What quantity did you compare to order them?

Mains voltage at home is $230\ \text{V}$ and that of a button cell battery is $3\ \text{V}$.

1. a) Which quantity are we comparing?
2. b) Explain, using the idea of "push" on charges, why the mains electricity grid is dangerous while a button cell battery is not.
3. c) The human body offers a certain resistance to the flow of current. Using this idea, reason what will happen if the voltage we touch is much higher.

What electrical quantity indicates the amount of charge that passes through a wire every second? In what unit is it measured in the International System of Units?

The manual of a toy drone states that its motors draw $500\ \text{mA}$.

1. a) Express this current in amperes.
2. b) Does it draw more or less current than a bulb through which $0,6\ \text{A}$ passes?

A portable fan has four $1,5\ \text{V}$ batteries connected one after another, as shown in the figure, and the combination supplies $6\ \text{V}$.

1. a) Which quantity adds up when connecting the batteries like this?
2. b) Explain this result by imagining several water pumps placed one after another in the same pipe.
3. c) What voltage would the combination give if we removed one of the batteries?

All components in a circuit oppose the flow of current to a greater or lesser extent. What quantity measures this opposition? In what unit is it expressed?

Water flows easily through a wide, short pipe; through a narrow, long pipe it flows with much more difficulty.

1. a) Which of the two offers more resistance to the flow of water?
2. b) Apply this idea to two copper wires, one short and thick and the other long and thin: through which one will the current flow better? Justify your answer.

We connect a copper rod and a pencil lead (graphite) of the same size separately to the same battery along with a light bulb: with the copper, the bulb shines clearly brighter.

1. a) Which of the two materials has higher resistance? How do you know?
2. b) Would you say that graphite is a conductor or an insulator? Justify your answer based on what was observed.
3. c) Suggest a reason why wire sheaths are made of plastic and not graphite.

In the laboratory, we use a device that can measure voltage, current, and resistance depending on the position of its dial.

1. a) What is it called?
2. b) Which unit would you select with the dial to test a toy's $4,5\ \text{V}$ battery?

Observe the circuit in the diagram, showing the two possible placements (A and B) of the multimeter.

To measure the voltage across a bulb connected to a battery, where do we place the two probes of the multimeter: touching both terminals of the bulb or disconnecting a wire and inserting the device into the circuit? Explain what the multimeter measures in each placement.

Observe in the figure how the ammeter and the voltmeter are connected.

The ammeter is connected in series within the circuit so that all the current passes through it.

1. a) Reason whether its internal resistance should be very high or very low, considering what would happen to the current we want to measure.
2. b) The voltmeter, on the other hand, is connected across the two terminals of the component. Reason whether it should have a high or low internal resistance, considering which path the current will prefer to take.