8 grade. 7 lab. Lesson

The title of the laboratory work: Measurement of work and power of the electric current

Purpose of the work: 

• Identify the power of the lamp using ammeter and voltmeter;
• Calculate the work of the electric current in the lamp;
• Identify the cost of the electric current according to the current tariff.

Expected results:

• The work and power are directly proportional to the current strength and the voltage.

Teacher’s Guide:

• Divide the students to 3 students in each group.
• Before starting laboratory work, read the safety rules:

• To download the worksheet, please follow this link:

Theoretical part

The work of electric current on a part of an electric circuit is equal to the voltage at the edges of this part, the current strength and time it took for the work to be done. The formula is:

The power – is a physical quantity, that is equal to the work done by electric current to the unit of time:

The cost of electric current depends on the tariff per 1 kWh, it is identified by the formula:

where Cm – is the cost, A – work, T – current tariff.

Sources:

1. Работа и мощность электрического тока. (2018). Физика. Учебник для 8 класса общеобразовательной школы. 

Experimental part

Experiment 1. Identifying the power of the lamp. 

Procedure:

Step 2. Write down the nominal values of the current and voltage indicated on the base of the lamp in the table.

Step 3. Calculate the power values according to the results of the experiment and by the nominal values of the current and voltage:

Considering the results, draw a conclusion.

Experiment 2. Identifying the work of the electric current and its cost.

Procedure:

Step 1. Calculate the operation of electric current in SI units in 1 hour, 1 day and 1 month, using the formula for calculating the operation of the current.

Enter the results in the table. Express the result in kW h.

Step 2. At the current tariff, calculate the cost of electricity:

Step 3. Determine the cost of electricity spent on the uninterrupted operation of the garland of 40 lamps for a month. Analyze the calculations and conclude.

Research part

U, V	I, А	P, W	Un, V	In, А	Pn, W

Time	Work А, J	Work А, kW h	Tariff Т, tenge	Cost Сm., tenge
1 hour
1 day
1 month

When deriving conclusions, answer the following questions:

• How is the work associated with the current power in the circuit? How can it be measured?
• What is current power? How is it related to the main characteristics of the circuit: current strength and voltage?

Conclusion

The work  and power of electric current is directly proportional to the current strength and voltage.