Comprehensive Study Guide on Electrical Voltage, Circuits, and Power

Basics of Voltage and Electrical Sources

To establish an electrical circuit, a voltage source is an absolute requirement. Common examples of these sources include batteries, accumulators (rechargeable batteries), and dynamos. Additionally, the solar panels equipped with zonnecellen (solar cells) frequently seen on rooftops function as voltage sources. Every battery or accumulator has its supplied voltage explicitly stated on its casing, with typical values being $1.5\,V$, $9\,V$, or $12\,V$. This stated voltage can be verified using a spanningsmeter, which is commonly referred to as a voltmeter because voltage is measured in the unit Volt ($V$). To perform a measurement, the voltmeter must be connected to both the positive pole (pluspool) and the negative pole (minpool) of the battery.

Voltage can be conceptualized by comparing it to the air pressure in an inflated balloon. A balloon that is fully inflated possesses high pressure or "voltage," which can be felt as the rubber becomes tightly stretched and resistant to being pushed. Conversely, a balloon that is only half-full has much lower tension, and the rubber yields easily. If there is no air, there is no tension or voltage. This relationship is illustrated in Figure 1, which demonstrates that the more air contained within the balloon, the greater the resulting tension or voltage.

Voltage, Current, and Energy Transfer

When the valve or nozzle of an inflated balloon is opened, air begins to flow out, causing the internal pressure to drop. This flow is analogous to electrical current. Current strength (stroomsterkte) is defined as the specific amount of air or charge that flows out of the source per second. As the pressure (voltage) decreases, the current strength also diminishes until the voltage is entirely depleted and the flow stops.

Energy transfer can be observed by using the energy from flowing air to rotate a windmill, as shown in Figure 2. In this scenario, energy is transferred from the air to the blades of the mill. When comparing two balloons with the nozzle opened equally, a balloon with high voltage imparts more energy to the air than one with low voltage. Consequently, a higher voltage results in more energy being transferred to the connected components. In electrical systems, the voltage of a battery indicates the amount of energy provided to the flowing charge. A battery rated at $3.0\,V$ provides exactly twice as much energy to the same amount of charge as a battery rated at $1.5\,V$. This energy is then transferred to devices, such as a light bulb, within a closed circuit.

Capacitors and Constant Voltage Sources

An electrical component known as a capacitor (condensator) behaves similarly to a balloon. It can be charged by storing electrical charge within it, causing the voltage to rise until it can no longer hold more charge. When the charge is allowed to flow out, the voltage drops—initially at a rapid pace and then progressively slower over time (as seen in Figure 4). While capacitors are widely used in electronics to protect components from sudden voltage fluctuations, they are not suitable for powering devices continuously. This is because a capacitor does not provide a constant voltage; a lamp connected to one would steadily dim and eventually go out.

In contrast, batteries and accumulators are designed to provide a constant voltage, which is why they are characterized as reliable voltage sources. Even as charge flows into a circuit, the voltage of a battery remains steady because chemical reactions occurring inside the battery continuously release new charge. These are known as chemical voltage sources. These reactions consume internal substances to produce charge, and when these primary materials are nearly exhausted, the battery can no longer maintain its voltage, leading to the designation that the battery is "empty."

Standard batteries are intended for single use and must be discarded after their energy is spent. However, reusable or rechargeable batteries exist. These can be restored by passing an electrical current through them in the reverse direction. This process reverses the chemical changes, causing the substances formed during discharge to disappear and recreating the original materials for reuse. In non-rechargeable batteries, these chemical changes are irreversible.

Connecting Batteries in Series

Applications often require more voltage than a single battery can provide. For example, a remote control may require two $1.5\,V$ batteries. To achieve the necessary voltage, these batteries must be connected in series. This configuration involves connecting the positive pole of one battery to the negative pole of the subsequent battery. When connected in series, the individual voltages are summed together. Therefore, two $1.5\,V$ batteries provide a total of $3.0\,V$, while four such batteries in series provide $6.0\,V$. Generally, the rule states that if you connect batteries in series, you may add their voltages together. However, if one battery in a series of four is accidentally placed in the wrong direction, it works against the others. In that case, the total voltage calculation would be $1.5 + 1.5 + 1.5 - 1.5 = 3.0\,V$.

Safety, Transformers, and the Environment

In the Netherlands, the standard mains voltage (netspanning) is $230\,V$. This level of voltage is dangerous; touching a conductor at $230\,V$ can result in a painful shock or even death. Because of this risk, appliances running on mains power must be heavily insulated to prevent contact with energized parts. Batteries, however, operate at much lower voltages that are considered safe to touch, typically below the safety threshold of $24\,V$. Most handheld devices like phones operate far below this limit. To connect these low-voltage devices to a $230\,V$ outlet, a transformator (transformer) is used. This component, often found inside a phone's charging adapter, converts the high mains voltage of $230\,V$ into a lower, safer voltage, such as $5\,V$.

Batteries have a significant environmental impact. While toxic substances like mercury and cadmium have been largely removed from modern batteries, they still contain materials harmful to the environment and must be disposed of as small chemical waste (klein chemisch afval). Rechargeable batteries are environmentally preferable because they can be reused hundreds of times, especially if charged using sustainable electricity from sources like solar panels. At the end of their lifecycle, both types of batteries should be recycled. Recycling allows specialized companies to extract valuable materials such as nickel ($Ni$), copper ($Cu$), and cobalt ($Co$), which reduces both the waste pile and the need for new raw materials.

Circuit Symbols and Schematics

Electrical circuits can be designed in various ways using lamps, switches, wires, and voltage sources. To describe these designs clearly, experts use a schakelschema (circuit diagram) containing standardized symbols. Key symbols include lines for wires (snoer), a circle with an "A" for a stroommeter (ammeter), a circle with a "V" for a spanningsmeter (voltmeter), and specific icons for lamps, bells, motors, and LEDs. Switches are depicted as either open or closed, while power sources are represented by battery or outlet symbols. These schematics are vital for conducting experiments and are the first step in the industrial design of electronic devices, ensuring the most cost-effective and functional layout before production.

Series and Parallel Circuits

A series connection (serieschakeling) is characterized by a single, unbranched loop. Because there is only one path for the electricity, the current strength is identical at every point in the circuit. However, if one component, such as a lamp, fails, the entire circuit is broken and all other components stop functioning. Furthermore, the total voltage from the source is distributed across the components; if three identical lamps are used, each receives exactly one-third of the total source voltage (bronspanning). Series connections are most practical for switches, which must be in series with the device they control to open or close the entire circuit loop.

In contrast, most electrical appliances are connected in a parallel connection (parallelschakeling). This configuration provides three major advantages: each device can be operated by its own switch, the failure of one device does not affect the others, and every device receives the full voltage of the power source. A parallel circuit splits into multiple branches. At the points where the circuit branches (points 1 and 5 in Figure 6), the current strength is known as the total current strength. This total current divides among the branches; in a circuit with three identical branches, each branch carries one-third of the total current. Unlike series circuits, the current strength in a parallel circuit is not equal at all points.

Mixed Circuits and Reasoning

A gemengde schakeling (mixed circuit) incorporates both series and parallel elements. For example, if two lamps are connected in parallel with each other but are collectively in series with a third lamp, they form a mixed circuit. The behavior of such a circuit depends on where a break occurs. If the main series lamp is removed, the entire circuit is interrupted. However, if one of the parallel lamps is removed, the remaining series lamp and the other parallel lamp will stay lit because a closed path remains. In terms of current, the series lamp will glow brighter because the entire current for the parallel branches must pass through it, meaning it handles the sum of the currents from the parallel sections.

Power and Efficiency

The longevity of a device's battery life depends on its efficiency. Power (vermogen) is the measure of how much electrical energy a device consumes per second. High-power devices, like laptops, consume more energy in a given time than lower-power devices like tablets. Power is typically measured in Watt ($W$), though milliwatt ($mW$) and kilowatt ($kW$) are also used. For devices with variable energy use, the maximum power value is usually listed. Some devices, like flashlights, have constant power, while others, like smartphones, have varying power needs depending on whether they are on standby or in active use for calls and internet.

Electrical power is determined by two factors: the voltage ($U$) at which the device operates and the current strength ($I$) flowing through it. This relationship is defined by the formula: $P = U \times I$ In this equation, $P$ represents power in Watt ($W$), $U$ represents voltage in Volt ($V$), and $I$ represents current strength in Ampere ($A$). This is comparable to the balloon and windmill analogy: a windmill's rotation speed depends on both the air pressure (voltage) and the amount of air flowing per second (current).

Battery Capacity and Management

To maximize the operational time of battery-powered devices, designers select energy-efficient components and use software to manage power consumption, such as by turning off screens after a period of inactivity. The capacity ($C$) of a battery indicates how much total charge it can store and is usually expressed in milliampere-hour ($mAh$). The capacity is calculated by multiplying the current supplied ($I$) by the time ($t$) the battery can provide that current: $C = I \times t$ In this formula, $C$ is the capacity in $mAh$, $I$ is the current strength in milliampere ($mA$), and $t$ is the time in hours ($h$). For example, a battery with a capacity of $2000\,mAh$ can sustain a current of $10\,mA$ for $200\,h$, a current of $100\,mA$ for $20\,h$, or a current of $500\,mA$ for only $4\,h$ before it is empty.