Electricity. It's everywhere. You use it every day at home as you turn on lights, use appliances, then when you get in your car and turn the ignition switch, electricity is in the computer on which you are reading this.
All these experiences and countless more involve the movement of electric charges around a close path that we call an electric circuit. Circuits are essential for being able to use electric energy.
In this PhysicsQuest you will take a look at the basic elements of circuits and how they work. You will also learn about the hazards of electricity and the various factors affecting them.
This PhysicsQuest is divided into three parts:
Part I. Series and Parallel Circuits.
You will use a computer simulation to understand how electric circuits work.
Part II. Electric Hazards.
You will read each section by clicking on the links provided and answering the questions given.
Part III. Measuring Current and Voltage.
In this section you will learn how voltmeters and ammeters work.
PROCESS AND RESOURCES
PART I.SERIES AND PARALLEL CIRCUITS
An electric circuit is formed when a conductive path is created to allow free electrons to continuously move. This continuous movement of free electrons through the conductors of a circuit is called a current, and it is often referred to in terms of "flow," just like the flow of a liquid through a hollow pipe.
PART III. DC VOLTMETERS AND AMMETERS
Any device used to detect an electric current is called a galvanometer. Many important DC measuring instruments use a galvanometer as an indicating element. Two of the most common are the voltmeter and the ammeter.
8. Explain what a voltmeter measures and why it must be connected in a specific manner in a DC circuit.
9. Explain what an ammeter measures and why it must be connected in a specific manner in a DC circuit.
What drives current? We can think of various devices such as batteries or generators which are necessary to maintain a current. All such devices create a potential difference or voltage.
When a voltage source is connected to a conductor, it applies a potential difference that creates an electric field. The electric field in turn exerts force on charges, causing current. .
Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance. The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow. Ohm’s Law relates these three quantities in a meaningful way.
The two simplest ways of connecting resistors are in series and parallel. Resistors are in series whenever current must flow through them sequentially. Resistors are in parallel when each resistor is connected directly to the voltage source.
- Print the worksheet:
- Go to the OHM ZONE and use the simulation to answer the questions on the handout.
PART II.ELECTRIC HAZARDS
There are two known hazards of electricity - thermal and shock. A thermal hazard is one where excessive power causes undesired thermal effects, such as starting a fire in the wall of a house. A shock hazard occurs when electric current passes through a person. Shocks range in severity from painful, but otherwise harmless, to heart-stopping and lethal. This section considers the factors affecting shock hazards and the systems and devices for preventing them.
1. Read the explanation and the physiological effects of electric shocks. Discuss the factors that affect the severity
10. What modifications are needed to convert a galvanometer into a voltmeter?
11. A certain galvanometer has an internal resistance of 30 ohms and gives a full-scale deflection for a current of 1 mA. Calculate the multiplier resistance necessary to convert this galvanometer into a voltmeter that has a maximum range of 50 V. Show all your work!
12. What modifications are needed to convert a galvanometer into an ammeter?
13. A certain galvanometer has an internal resistance of 46 ohms and a current of 200 mA is required for full-scale deflection. What shunt resistance must be used to convert the galvanometer into an ammeter whose maximum range is 10 A? Show all your work!