Powering Earth

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Question 10
Medium

A group of students compare the power of three electrical immersion heaters X, Y and Z using this method:

  • They place each heater into a container of water.
  • They plug the heaters in and switch them on.
  • They measure the temperature of the water every 30 s.
  • They calculate the change in thermal energy of the water every 30 s.
a.

Each heater has the same efficiency and is used for the same length of time.

Describe one other factor the students should control in their method to make it a fair test.

[1]
b.

The students test the heaters using a valid method.

The graph below shows how the change in thermal energy of the water varies with time for each heater:

A line graph with 'Time (seconds)' on the horizontal x-axis labeled from 0 to 120 in increments of 20, and 'Change in thermal energy (joules)' on the vertical y-axis labeled from 0 to 200,000 in increments of 20,000. Grid lines are present. Three straight lines originate at the origin (0,0): Heater X is represented by a dash-dot line ending at coordinates (120, 180,000). Heater Y is a solid line ending at coordinates (120, 120,000). Heater Z is a dotted line ending at coordinates (120, 60,000).

Each heater has the same efficiency.

Use data from the graph to:

  • Describe in detail how the change in thermal energy varies with time.
  • Compare the power of the three heaters, including calculations of their power.
[5]
c.

How is electrical energy transferred from the power station to the school's mains sockets?

In your answer, write about:

  • How electricity is distributed across the country.
  • The type of voltage/current used.
[4]

Powering Earth Questions

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