Exercises: The electrical circuit

Match each circuit component with its function: (a) battery, (b) wire, (c) light bulb, (d) switch. Functions: 1. conducts current from one component to another; 2. provides energy to the circuit; 3. opens or closes the current path; 4. transforms electricity into light.

Electric current is a flow of charge travelling along wires, similar to water flowing through a pipe. Explain the complete analogy: what the battery represents (the pump that pushes), what the wires represent (the pipes), and what the light bulb represents (a water wheel turned by the water).

The figure shows the diagram of a circuit with its standard symbols, but one of the components is covered with a question mark, as shown in the diagram.

Which component is missing from the circuit and what would happen if it were not there? Name the other components in the diagram and describe what happens when the switch is closed.

True or false? Justify each answer: (a) without a battery or another power source, there is no current; (b) with the switch open, the light bulb shines just the same; (c) the light bulb is a load because it transforms electricity into light; (d) the wires must form a closed path for current to flow.

A switch and a push button do not do the same thing: one stays fixed in position and the other only works while pressed. Match each component with its use: (a) a room light; (b) a doorbell. Explain what would happen if we swapped them.

Classify these components into power sources, conductors, output devices/loads, control devices or protective devices: battery, wire, motor, fuse, two-way switch, buzzer. Explain in one sentence the function of each of the five groups.

The figure shows the standard symbols for eight circuit components, but the name of one is covered, as shown in the diagram.

Which component corresponds to the symbol with the covered name? Write down the symbol-component pairs for all eight, and explain why circuit diagrams use symbols instead of realistic drawings of the parts.

What is a short circuit? Explain it in your own words (current finds a direct path without passing through any load) and reason why it is dangerous: what happens to the wires and the battery when current flows without any 'obstacle' to use it.

Draw in your notebook the diagram of a circuit with a battery, a switch and a light bulb using standard symbols. Then describe the path current takes when you close the switch and what happens when you open it.

You can do it on paper and send a photo with your answer.

The figure shows two circuits, each with a battery and two light bulbs connected differently, as shown in the diagram.

In the circuit on the left, the light bulbs are in series (a single path for current), and in the one on the right, in parallel (a path for each bulb). What happens in each circuit if one of the bulbs blows? Reason why it is better to connect the lights of a model in one of these two ways.

A doorbell is a circuit with a battery, a push button and a buzzer. Describe how it works completely (what happens when the button is pressed and when it is released) and explain why a push button is the suitable control component for a doorbell rather than a switch.

A hallway light is turned on and off from two different places using two two-way switches. Explain in your own words how this is possible (each two-way switch changes the current path between two options) and why this could not be achieved using two standard switches.

A fuse is a protective device: if too much current flows, it melts and opens the circuit. Explain why a component that 'breaks' protects all the others, and what you should check if a fuse blows twice in a row.

A battery-powered fan has a battery, a switch and a motor. Identify the role of each component (power source, control, load), explain what energy transformation takes place when it operates, and what disadvantage connecting the motor directly without a switch would have.

'The circuit must be closed for current to flow.' Explain what this statement means using the water and pipes analogy, and give two examples of an 'open circuit' in your house (a switched-off switch, a blown light bulb), explaining at which point the path is interrupted in each case.

Your torch does not turn on. Order these checks from simplest to most complex, and explain which component each one inspects: broken switch, flat or incorrectly inserted batteries, blown light bulb, loose wire contact.

In the Technology workshop, you connect a light bulb to a 4,5 V battery and it shines with normal brightness. Next, you connect two identical light bulbs in series to that same battery and observe that they shine much less. Your classmate claims: «The first bulb takes almost all the current and the second one only gets what's left over; that's why they shine less». Refute your classmate's error with technical arguments, explaining what actually happens with the current and the distribution of the battery's energy, and reasonably predict what will happen to the brightness of each one if you add a third identical bulb in series.

Design the circuit for a scale model in which pressing a push button makes a buzzer sound and a light bulb turn on at the same time. Draw the circuit diagram using symbols in your notebook, decide whether the two output devices are in series or parallel, and justify your choice considering what happens if one of them breaks.

You can do it on paper and send a photo with your answer.

When you close the switch on your model, the light bulb does not turn on, but after a few seconds you notice that the battery heats up quickly and gives off a smell of hot plastic. Diagnose what type of fault is occurring in the circuit and explain at an electrical level why the light bulb remains off while the battery overheats. Describe the step-by-step procedure you would follow to inspect the assembly, locate visually or through testing the faulty section, and fix it safely.

To illuminate a Christmas model, you have a 4,5 V battery and several identical light bulbs designed to operate at 4,5 V. A classmate insists on connecting ten light bulbs in series "to save wire and make the battery last longer", while you propose connecting them in parallel. Compare what would happen to the brightness of the bulbs in each of the setups, what would happen in the circuit if one of them burns out during the exhibition, and how this would affect finding the broken bulb. Conclude which is the only viable option and defend your stance by refuting your classmate's arguments.

The figure shows the schematic of a circuit with a battery, a two-way switch, and two loads (a light bulb and a buzzer):

A classmate claims that if the bulb burns out, the buzzer will not be able to work either because both loads share the same battery, and that leaving the switch lever halfway will make the buzzer sound and the bulb light up at the same time. Analyze the circuit and technically refute both statements by following the paths of the current. Finally, propose a practical and justified use for this setup in a model.

The protective fuse of a workshop circuit has blown twice in a row this week as soon as it was connected. A classmate proposes: "So we don't waste any more time changing fuses, let's put in one with a thicker wire or wrap a piece of aluminium foil around it; that way the power definitely won't cut out again". Refute your classmate's proposal by explaining the exact safety function that the fuse performs, predict what physical and material consequences bypassing it with that improvised conductor would have if the fault persists, and detail the correct procedure you should follow before replacing it.

You have assembled a circuit with a new 4,5 V battery, crocodile clip leads, a closed switch, and a light bulb mounted in its socket, but the light bulb does not turn on. Design an orderly, step-by-step technical troubleshooting guide to safely locate the fault, identifying at least four different possible causes. Furthermore, justify why in the technical troubleshooting method it is essential to modify or check only one element at a time in each test.

The compartment of a remote control holds two 1,5 V batteries connected in series via a metal plate at the bottom. The manufacturer indicates placing one battery with the positive terminal facing up and the other facing down. Explain what function the metal plate performs and what total voltage the batteries supply to the circuit in that position. Next, predict what resulting voltage will reach the circuit if you put one of the two batteries in backwards and explain why the device will not work. Finally, technically distinguish this fault from the one that would occur if a wire were broken.

Topic Challenge. How does the lighting you use every day work, and what impact does it have on energy consumption? Become an electrical auditor for your home by following these phases:

1. Identify: Choose a flashlight or a portable lamp from home. Identify its four basic components (generator, conductors, load/receiver, and control device). Write down the nominal voltage of its batteries (for example, $1,5\text{ V}$ or $4,5\text{ V}$).

2. Simulate: Go to Tinkercad Circuits (a free web tool) and recreate this electrical circuit using basic symbology: battery, switch, and light bulb or LED. Verify that the circuit works by opening and closing the current path.

3. Analyze and propose: Check the real-time energy demand graph on the Red Eléctrica de España (REE) website. Write a short report (one page) that includes a screenshot of your Tinkercad circuit, an explanation of how the current flows, and two reasoned proposals to reduce electricity consumption in your home by replacing loads/receivers.

Assessment criteria:

• Correct identification of the four circuit elements and their electrical magnitudes ($V$).

• Functional simulation and correct interconnection of components in Tinkercad.

• Analysis of real REE data and technical consistency in the energy-saving proposal.