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Solving Exercise 1, page 47, Grade 9 Physics Textbook
Exercise:
A functioning electric stove has a resistance of R = 80Ω and a current intensity through the stove of I = 2.5A.
a) Calculate the heat released by the stove in 1 second.
b) Using the electric stove to boil 1.5 liters of water with an initial temperature of 25°C takes 20 minutes. Assuming the supplied heat for boiling water is useful, calculate the efficiency of the stove. Given the specific heat capacity of water is c = 4,200J/kg.K.
c) Using this electric stove for 3 hours every day, calculate the electricity bill for using the stove for 30 days, if the price of 1kW.h is 700 dong.
Solution:
Solving Exercise 2, page 48, Grade 9 Physics Textbook
Exercise:
An electric kettle marked 220V - 1000W is used with a voltage of 220V to boil 2 liters of water from an initial temperature of 20°C. The efficiency of the kettle is 90%, where the heat supplied to boil water is considered useful.
a) Calculate the heat required to boil the given amount of water, knowing the specific heat capacity of water is 4,200J/kg.K.
b) Calculate the heat released by the electric kettle.
c) Calculate the boiling time of the given amount of water.
Solution:
Solving Exercise 3, page 48, Grade 9 Physics Textbook
Exercise:
A power line from the common power grid to a household has a total length of 40m and a copper core with a cross-sectional area of 0.5mm². The voltage at the end of the power line (at home) is 220V. This household uses hairdryers and light bulbs with a total average power of 165W for 3 hours each day. Knowing the resistivity of copper is 1.7 x 10^-8 Ω.m.
a) Calculate the total resistance of the power line from the common power grid to the household.
b) Calculate the current intensity flowing through the power line when using the given power.
c) Calculate the heat dissipated on this power line over 30 days in kW.h units.
Solution:
Exercises on electric power and energy consumption are important lessons in Chapter I - Electricity. Let's explore hints for solving exercises on pages 40 and 41, Grade 9 Physics, to grasp the knowledge better.
In Chapter I - Electricity of Grade 9 Physics, students study the Electric Power - Work of Electric Current lesson. It is essential for students to solve exercises on pages 37, 38, 39 of Grade 9 Physics before attending class to improve their understanding of Physics.
