Praxis Elementary Education Exam— Energy and Matter

The Science section of the Praxis Elementary Education exam may contain questions about the interaction of energy and matter. There are several ways that energy can interact with matter:

• Sound: Waves made by vibration passing through the matter of air. The faster the vibration, the higher the pitch. Shorter (more compressed) wavelengths carry more energy so they vibrate at a higher frequency.
• Nuclear energy: Stored in the nucleus of an atom. The energy may be released through fusion, when two or more nuclei are combined (as in a hydrogen bomb), or through fission, when the nucleus of an atom is split (as in a reactor or an atomic bomb).
• Magnetic energy: A force that pulls or pushes across a distance by opposing or like poles, respectively. A north pole (N) pulls a south pole (S), and vice versa, but two N poles repel, as do two S poles.
• Light: Electromagnetic waves produced by fast-moving electrons releasing energy. Light waves are transverse, occurring in a series of up-and-down oscillations. When the rays of light waves bounce off a surface, it is a reflection. When light rays bend passing through a medium, such as water, it is refraction. The color we see is the color—frequency—of the spectrum NOT absorbed by an object. A ripe orange absorbs all the colors except orange, reflecting that color back out.
• Electric energy: Produced when electrons move through a conductor along a closed circuit, as shown here.

Because electrons have a negative charge, they move toward a positive charge (opposite charges attract). Electric energy may produce heat, light, motion, or a magnetic force. Static electricity is an accumulation of charges (positive or negative) on an object. Units of measurement include the voltage (volt), measuring electrical pressure, and the ampere (amp), measuring the rate at which the current flows.

Practice question

1. Which of the following is true? A. A circuit needs just to be closed and to have a conductor in order for heat or light to be produced. B. You can hear sound in outer space. C. A prism is an example of reflection. D. A compass's North points towards the North (directional) Pole of the planet. So, in reality, Earth's North directional pole is its South magnetic pole.

Answer and explanation

1. The correct answer is Choice (D). Earth is a magnet and thus reacts with other magnets in this opposites-attract manner. Choice (A) is not true because there must also be a source (of energy) such as a battery. Choice (B) is not true because there is no matter, no air, for the energy to interact with and produce vibrations (of the air molecules). Choice (C) is not true because when (white) light passes through a prism, the light is refracted, or bent, and the different colors, traveling at different frequencies, exit the prism at different speeds.