## Conductivity

### XVI. Science and Technology/Engineering, Grade 5

##### Question 9: Mark built an incomplete circuit with a light bulb, as shown below.

As the Standardized Test Season continues, here is another sample question taken, this time, from the 5th Grade 2014 MCAS exam.

## 1.  Electrons

The “uncuttable” atom is composed of a relatively enormous core of positively charged particles lost is a cloud of minute, mercurial negatively charged electrons moving faster than the eye can see. These tiny particles use every bit of their energy trying to escape each other and the core. Depending on how possessive the core is, some electrons on the outskirts of an atom can be the recipient of enough energy to pull away, if only for a fraction of a second, then release this fleeting burst to a neighboring electron. This is the movement of an electric charge. This is electricity.

## 2.  Electricity

The flow of charge via high energy electrons, in any material, is called current. Note the water metaphor. Like water, electron flow requires a potential difference. In the figure provided in the exam question above, the source of potential difference is the battery or voltaic cell. Yes, Volt, Voltaic as in Alessandro Volta (1745-1827). Saving the chemistry that powers the cell for another day, when the circuit is closed, the potential difference across the battery draws electron through the wire and the light bulb toward the positive pole.

## 3.  Conductors and Insulators

Super simple rule of thumb, metals conduct electricity and non-metals resist or insulate against it. Reality is, however, never simple. Different metals have vastly different conductivities and non-metals, depending on temperature and pressure, CAN be conduits for charge transfer. As with the battery’s chemistry, this topic is best left for a discussion at an AP or College Physics level.

Essentially, as stated earlier, atomic “possessiveness” is the key.

Most metal atoms have a lot going on. Therefore, the frenetic outer electrons are more likely to run wild. Insulators, however, have more time on their hands so they keep their electrons close to home.

So, electricity is a function of opportunity.

Are the electrons flapping in the breeze ready for a low five,

Or are they being held close to the vest.

Now, getting back to our questions……and the answers.

a. Identify each object from the list as a conductor or insulator of electricity.

– Copper Nail: Strong Conductor

– Glass Lens: Insulator

– Steel Spring: Weak Conductor

– Wooden Block: Insulator

b. Identify what will happen to the light bulb when each of the objects is placed in the circuit.

– Copper Nail: Lights Brightly

– Glass Lens: Remains Unlit

– Steel Spring: Lights Dim

– Wooden Block: Remains Unlit

c. Explain why conductors and insulators produce the results you identified in part (b).

See above discussion.

Visualized Physics (1940)

Alexander Taffel (Author)

Oxford Book Company

NY NY

The Cartoon Guide to Physics (1991)

Larry Gonick (Author),Art Huffman (Illustrator)

HarperCollins Publishers

NY NY 10022