Electricity: Keeping safe

Electricity: Keeping safe

Pencil and paperOnline interactive
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about conducting electricity and safety.

Question

 

 

 line carrying 11,000 volts
a)  How is it that a bird can perch on a high-voltage power line without being electrocuted?
     Select the answer below you think is right

    • "Birds' claws don't conduct electricity."
       - Ani

    • "Only humans get electrocuted."
       - Cam

    • "It is easier for the electricity to travel along the wire than through the bird."
       - Ihipera

Question

b)  Select the pictures where there is a danger of being electrocuted.

c) Explain how the electricity will travel in one of the pictures you chose.
Task administration: 

This assessment task could be used as a group assessment. The range of possibilities for question a) should promote discussion. Each group could come to a decision and be prepared to justify it. Listening to students' ideas will give extra information about their thinking.

Level:
4
Curriculum info: 
Science, Knowledge, Physical World
Keywords: 
physics concepts, energy, electricity, safety, group assessment
Description of task: 
Task: Select the correct reason why a bird on a power line does not get electrocuted and select pictures of danger of electrocution, justifying choice. Assessment focus: understanding of the route taken by electricity/electrocution.
Making Better Sense: 
Currents
Answers/responses: 
 

Y5 (03/2003)
a)
"It is easier for the electricity to travel along the wire than through the bird."
 - Ihipera
 moderate
b)         easy
c) Answer mentions electricity travelling through the object, through the person, and to the ground, e.g., any 1 of:

  • The electric current will travel through the boat / person to the ground when the mast touches the power lines.
  • The electric current will travel through the boy to the ground.
  • The electric current will travel through the kite to the person and then the ground, if the kite touches the power lines.

Answer mentions electricity travelling through the object, through the person, but not to the ground.

 very difficult

 
 
 
 

moderate
Diagnostic and formative information: 

Concept: electricity will always take the easiest route.

  • Referring students back to their experiences with simple circuits may be a helpful strategy to use. Get them to make up a simple circuit, and explore what materials can cause a short, by challenging them to stop the bulb glowing without removing anything from or breaking the circuit.
Concept: the human body can be included in a circuit.

  • Ghost balls are useful for demonstrating this. Students form a circle by holding hands and those on each side of the ghost ball touch the terminals to set it off. Discuss why in this case there is no "shock" (the voltage is very small, especially compared to the 11 000 volts of some power lines).
  • Explore how an electric fence works. Discuss how the electricity flows round the circuit. What happens to the electric current when the fence wire is touched? What do the insulators on the posts do?

For question a) almost half the trial students chose Birds' claws don't conduct electricity. One student mentioned that this was because birds have rubbery pads on their feet. This student is applying knowledge about insulating materials, and is partly correct (although not about the birds' feet being made of rubber). Electricity can pass through birds' feet, but the power lines are much better conductors. It is easier for the electricity to go through the wire.

For question c) 48% of the trial students mentioned the electricity travelling through the object to the person, but almost all omitted electricity passing through the person to the ground/earth in their explanation. (Both the human body and the earth are good conductors of electricity - it is when the current travels through the body that electrocution occurs. Electricity will always take the route of least resistance.)

Almost 25% said that the person would be electrocuted or zapped, but did not explain how this would occur. This type of answer indicates that the student knows the result, but has not demonstrated that they understand the science, why it happens.