8TH GRADE PRACTICE
Physics Problems: Work and current power, Grade 8
Electrical energy, heating and safety.
Here the conditions and analysis of the solution can be read without an account. In the simulator, you need to collect the same analyzes yourself: “Given,” formulas, order of steps and answer.
Problem statements
The answer options are there to check against, and the walkthrough opens under each problem.
Problem #55
Operation, power and energy consumptionEvaluate the statement: Energy transferred by an electric field to charges and converted by a device into other forms.
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At constant voltage and current, work is equal to their product times time.
Answer
Problem #56
Operation, power and energy consumptionEvaluate the statement: The concept “Electric current power” means: A household meter measures the work done by a current, usually expressed in kilowatt-hours.
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The power on the device plate helps to estimate the current, energy consumption and permissible network load.
Answer
Problem #57
Current workThe lamp operates at a voltage of 220 V and a current of 0.5 A for 120 s. Find the power and work of the current.
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Answer
Problem #58
Thermal effect of current and safetyEvaluate the statement: The amount of heat in a conductor is equal to the product of the square of the current, resistance and time.
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Doubling the current quadruples the heat, so overloading the wiring is especially dangerous.
Answer
Problem #59
Thermal effect of current and safetyEvaluate the statement: The term “Short Circuit” means: Safe operation requires proper insulation, grounding, protective devices and absence of contact with live parts.
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A fuse or circuit breaker breaks the circuit before the wires overheat and a fire occurs.
Answer
Problem #60
Joule-Lenz lawA current of 2 A flows through a 5 Ohm resistor for 60 s. How much heat will be released?
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Answer
The theory behind these problems
Work through the topic if a problem will not give in.
Formulas by topic
Look up symbols and units of measurement in the reference.