Exploring simple circuits

Grade 9 Science 

Content

• Voltage, current and resistance
• Circuits

Curricular competencies

Questioning and predicting

• Demonstrate a sustained intellectual curiosity about a scientific topic or problem of personal interest
• Make observations aimed at identifying their own questions, including increasingly complex ones, about the natural world

Planning and conducting

• Collaboratively and individually plan, select, and use appropriate investigation methods, including field work and lab experiments, to collect reliable data (qualitative and quantitative)
• Ensure that safety and ethical guidelines are followed in their investigations

Processing and analyzing

• Seek and analyze patterns, trends, and connections in data, including describing relationships between variables (dependent and independent) and identifying inconsistencies
• Use knowledge of scientific concepts to draw conclusions that are consistent with evidence
• Analyze cause-and-effect relationships

Evaluating

• Evaluate their methods and experimental conditions, including identifying sources of error or uncertainty, confounding variables, and possible alternative explanations and conclusions
• Describe specific ways to improve their investigation methods and the quality of the data

Applying and innovating

• Transfer and apply learning to new situations
• Generate and introduce new or refined ideas when problem solving

Communicating

• Communicate scientific ideas, claims, information, and perhaps a suggested course of action, for a specific purpose and audience, constructing evidence-based arguments and using appropriate scientific language, conventions, and representations
• Formulate physical or mental theoretical models to describe a phenomenon

An electric circuit provides a continuous path for electricity to flow through. There are three parts to an electric circuit:

• An energy source, like a dry cell or battery, provides energy.
• A load, like a light bulb or resistor, is the object that uses the available electricity.
• A conducting material, like a wire, that connects the energy source to the load and provides a path for the electricity to flow.
• A switch is an optional fourth component that can be used to open or close the circuit.

The flow of electric particles is called electric current. Only the negatively charged particles, electrons, move through a circuit. Electric current refers to the amount of charge that passes a point in a circuit in a given time. The unit of measurement for electric current is the ampere (A), named after the French physicist André-Marie Ampère.

The typical amount of current flowing through a 100-watt incandescent light bulb is 1 A. CFL and LED bulbs use considerably less current. An average TV set draws 3 A of current, while a starter motor in a car uses 500 A. We can use an ammeter to measure the amount of electric current at any point in a circuit.

Each electron has electric potential energy. We can measure the electric potential difference, the increase or decrease in electric potential energy, by measuring the electric potential energy per coulomb of charge. A coulomb is the charge transported by a steady current of 1 ampere in 1 second. Electric potential difference, the amount of electric potential energy in every coulomb of charge, is called voltage, is measured in volts (V), and is measured by a voltmeter.

A voltmeter can be connected across a component in a circuit to measure voltage. Note that the voltmeter is connected in parallel to the component (providing an alternative path for the current) so that a small amount of current goes through the voltmeter and the rest of the current goes through the circuit path. Voltmeters can be either analog or digital. A multimeter can also be used to measure voltage.

When an electric current enters a load it converts that electrical energy. A light bulb converts electricity into heat energy and light energy.

Circuit diagrams use a universal set of symbols, so can be understood anywhere in the world. The symbols also make it easier to draw complicated circuit diagrams showing different components. 

• You can use the “Lab investigations and safety evaluation" rubric to guide your observation and assessment of your students during the activity.

Worksheet answer key:

Observations

Table B

Analysis

1. An electric circuit is a continuous path through which electricity can flow. Circuits are commonly found in devices that use electricity to perform tasks, such as powering a light source or providing heat.
2. The three parts of an electric circuit are:
   • An energy source, like a dry cell or battery, provides energy.
   • A load, like a light bulb or resistor, is the object that uses the available electricity.
   • A conducting material, like a wire, that connects the energy source to the load and provides a path for the electricity to flow.
   • A switch is an optional fourth component that can be used to open or close the circuit.
3. Successful circuits contain all three essential parts of a circuit configured in a closed loop. Successful circuits may differ in how they are configured:
   • The different components may be arranged in a different order.
   • The circuit may include more than one of any essential component, like two light bulbs instead of one.
   • The circuit may include one or more non-essential components like a switch.
4. If the circuit is a series, the voltage measurements are the same: Approximately 1.5 V when one dry cell is used and approximately 3 V when two dry cells are used. If the circuit is a parallel, the voltage will remain approximately 1.5 V.
5. Answers will vary. Good examples include appliances that are plugged in, like televisions, computers, lamps and refrigerators. Some students may also describe the electrical system of the entire home as a system of circuits. All circuits work by providing a closed loop that enables electric current to flow.

Conclusions

• Students should provide a reasonable explanation of how they created functioning circuits and they should report on the accuracy of their prediction. They should also provide some ideas of how circuits are used in the real world.