- 8808 2348
- hello.scienceofstudy@gmail.com
- Mon - Sun 9:00AM - 5:00PM
Before you read on, you might want to download this entire revision notes in PDF format to print it out for your child, or yourself to read it later.
This will be delivered to your email inbox.
Electricity powers so much of our daily lives, from the phones in our hands to the lights above us and the air-conditioners that keep us cool. But have you ever wondered how this energy travels through wires and components to make a bulb glow or a device work? In this topic, we will uncover the basics of DC circuits, explore how electricity flows through wires, and see how the arrangement of components affects current, resistance, and voltage.
Circuit diagrams are visual representations of electrical circuits that use standard symbols. Learning these symbols will help you understand how a circuit is arranged and how it works.
| Function | Symbol |
Battery (DC supply) | Supplies the circuit with electrical energy with current in one direction only. |
*The longer line represents the (+) terminal. |
AC supply | Supplies the circuit with electrical energy with a current that periodically changes direction. |  |
Lamp/Bulb | Electrical device that produces light. |  |
Light emitting diode (LED) | Electrical device that produces light when current flows in a specific direction. |
|
Switch | Opens or closes a circuit |
|
Resistor | Provides resistance to limit the flow of current within a circuit. |
|
Variable resistor/Rheostat | A resistor where resistance can be adjusted. |  |
Thermistor | A resistor where resistance can be changed with temperature. |  |
Potentiometer | A resistor that is used to adjust voltage within a circuit. |
|
Light-dependent resistor | A resistor where resistance can be adjusted with light. |  |
Ammeter | Measures electric current within a circuit. |  |
Voltmeter | Measures the voltage within a circuit. |  |
Fuse | Protects a circuit by breaking if the current is too high. |  |
Because protons determine the identity of an element, isotopes have the same chemical properties. However, their different numbers of neutrons give them different atomic masses and may affect some physical properties.
Voltage, current, and resistance are the three key factors that govern electricity. Voltage, also known as electromotive force, is the electrical pressure that pushes electrons through a circuit, and it is measured in volts (V). Current is the flow of electrons, measured in amperes (A), while resistance is the opposition to this flow and is measured in ohms (Ω).
These three quantities are related by Ohm’s law:
V = I x R
Where V = voltage, I = current and R = resistance.
Conventional current flows from the positive to the negative terminal of a battery through a complete circuit. Therefore, current can only flow when the circuit is closed and unbroken, allowing it to travel from the source, through the load such as a light bulb, and back to the source.
If there is a gap in the circuit, such as when a switch is open or a fuse is blown, the circuit is incomplete and current cannot flow. As a result, the current drops to zero.
In a complete circuit, the voltage of a battery (ε) is equal to the total voltage of all loads across the circuit system. How total voltage (Vtotal) is calculated depends on the arrangement of components within the circuit, which we will talk about later in this article.
Like water, electric current tends to follow the path of least resistance. Although exam questions often tell you to assume that the resistance of wires is negligible, resistance still exists in real circuits. If there is a path with much lower resistance, such as a shortcut in the circuit, current will flow through that path instead. This can result in a short circuit.
By Ohm’s law, V = I x R. In a short circuit, the resistance becomes very low while the voltage remains constant, causing the current to increase sharply. This can lead to dangerous effects such as overheating of wires, damage to circuit components, and even electrical fires. For this reason, engineers work carefully to prevent short circuits when designing electrical systems.
Electrical components can be arranged in either series or parallel circuits.
In a series circuit, components are connected within the same path. Hence, the same electrical current flows through every component. If one component fails, this immediately results in a broken circuit.
Current in a series circuit is constant across the entire circuit.
Hence, I1 = I2 = I3, as the same current flows through the entire circuit.
When multiple batteries are connected in series, the total voltage across the circuit is equivalent to the sum of every battery’s voltage.
Vtotal = εtotal = ε1 + ε2
Likewise, when multiple components are connected in series, the total voltage is equivalent to the sum of voltage of every component.
εtotal =Vtotal = V1 + V2
The total resistance, also known as the effective resistance (Reff), is the sum of resistances of all components within the series circuit.
Reff = R1 + R2
In a parallel circuit, components are connected across multiple branches. This allows current to split and flow along different branches. Hence, if the components of one branch fails, current can still continue to flow through the remaining complete branches.
The current flowing into a junction of a parallel circuit must be equal to the current flowing back out of the same junction.
I1 = I2 + I3
Voltage remains constant across all branches of a parallel circuit.
ε = V1 = V2
The total, or effective resistance, within a parallel circuit can be described with the following equation.
(1/Reff) = (1/R1) + (1/R2)
There are many other components that can be connected to a circuit to modulate current, resistance and voltage.
An ammeter measures current along any point of a circuit. It is always connected in series to the component whose current is to be measured. During exams, it is generally assumed that ammeters have negligible resistance, unless specified otherwise.
A voltmeter measures potential difference along any two parts of a circuit. It is always connected parallelto the component we are trying to measure. Like ammeters, you can assume that voltmeters carry negligible resistance, unless specified otherwise.
Potentiometers, also known as potential dividers, are used to divide an input voltage into varying ratios of output voltages. They are useful when the voltage from the battery is fixed, but a different voltage output is desired.
Fig 6. A basic potentiometer consists of a dial that allows the output voltage to be adjusted by changing the resistance on either side of the wiper.
A transducer is a device that converts one form of energy to another.
Input transducers (sensors) convert non-electrical energy into electrical energy. Some examples include microphones (kinetic energy from sound waves into electrical energy), thermistors (thermal/internal energy into electrical energy) and light-dependent resistors (light intensity into electrical energy).
Thermistors and light-dependent resistors (LDRs) in particular modulate electrical energy output by changing resistance based on thermal or light energy input. Negative temperature coefficient (NTC) thermistors and LDRs decrease resistance in response to increases in temperature and light intensity respectively.
Output transducers (actuators) convert electrical energy into non-electrical energy. Some examples include speakers (electrical energy into sound), motors (electrical energy into kinetic energy) and LEDs (electrical energy into light).
A fuse is a crucial safety component within a circuit. Earlier, we have learned that short circuits drastically increase the amount of current flowing within a circuit, which can lead to dangerous outcomes. A fuse contains a thin wire which melts and breaks a circuit in the presence of excessive current. After use, the fuse must be replaced.
In this article, we have covered the basics of electricity and circuits. Since electricity is such a vital part of everyday life, it is important to understand and appreciate how electrical energy is managed and harnessed to power the world around us. With this knowledge, you may even pick up useful technical skills or one day become an electrical engineer.
Find out more by joining us at Science of Studying!
Prepared by: Michelle
You might want to download a pdf copy of this article for future reference!
Click the white download button below, enter your email, and the pdf file will be delivered to your inbox! (Remember to check spam!)
The Science of Studying provides live online tuition via Zoom classes for Combined/Pure Chemistry, Biology, and Physics. To date, we have taught 800+ students over 12 years.
In case you are wondering, yes – there is a science behind studying!
At Science of Studying, we use our SOS system™ to teach our classes so that even last-minute students can see remarkable improvements in their grades – without mind-numbing memorisation of textbooks and without the drudgery of doing numerous assessment books.
All these conducted in a fun, interactive, stress-free online environment.
If you need help with your Chemistry, Biology, and Physics subjects, do reach out to us and we will see what we can do to help.
Contact Us: Click Here
Admin number: +65 88082348
The SOS system™️ guides students through an effective process of:
Join our proven online tuition programs and see real improvements in understanding, confidence, and school results.
Book a free trial lesson and start the journey today or discover more below:
or
Open
Closed
or
or