Electrodynamics – Electric current – Electric energy – Electric power – EN
ELECTRODYNAMICS – ELECTRIC CURRENT – ELECTRIC ENERGY – ELECTRIC POWER
Electrodynamics
Electric current – Electric energy – Electric power
01-(ENEM-MEC)
A curious student, excited by the electrical circuit class he attended at school, decides to dismantle his flashlight. Using the bulb and battery removed from the equipment, and a wire with the ends stripped, he makes the following connections with the intention of turning on the lamp:
Based on the diagrams shown, in which cases did the lamp come on?
A. (1), (3), (6)
B. (3), (4), (5)
C. (1), (3), (5)
D. (1), (3), (7)
E. (1), (2), (5)
02-(ENEM-MEC)
The average distribution, by type of equipment, of electricity consumption in homes in Brazil is shown in the graph.
In association with the graph data, consider the variables:
I. Equipment power.
II. Hours of operation.
III. Number of equipment.
The value of the percentage fractions of energy consumption depends on
03-(ENEM-MEC)
Among the numerous recommendations given for saving electricity in a home, we highlight the following:
– Replace incandescent light bulbs with compact fluorescent ones.- Avoid using the electric shower with the switch in the “winter” or “hot” position.
– Accumulate a quantity of clothes to be ironed with an electric iron at once.
– Avoid using multiple sockets to connect several devices simultaneously.
– Use wires with diameters recommended for their intended purpose in the electrical installation.
The common feature of all these recommendations is the proposal to save energy by trying to reduce, on a daily basis,
a) the power of electrical appliances and devices.
b) the time of use of the devices and appliances.
c) the consumption of electrical energy converted into thermal energy.
d) the consumption of thermal energy converted into electrical energy.
e) the consumption of electrical energy through leakage currents.
04-(ENEM-MEC)
“…Brazil has the potential to produce at least 15 thousand megawatts per hour of energy from alternative sources.”
In the southern states alone, the potential for generating energy through agricultural and forestry waste is 5,000 megawatts per hour.
To get an idea of what this represents, the Ita hydroelectric plant, one of the largest in the country, on the border between Rio Grande do Sul and Santa Catarina, generates 1,450 megawatts of energy per hour.”
This text, transcribed from a widely circulated newspaper, contains at least ONE CONCEPTUAL ERROR when presenting production values and energy generation potential. This error consists of
a) present very high values for the energy quantity.
b) use the megawatt unit to express power values.
c) use electric units for biomass.
d) using the incorrect unit megawatt per hour.
e) present numerical values incompatible with the units.
05-(ENEM-MEC)
Please see the following table. It contains the technical specifications contained in the supplied instruction manual.
by the manufacturer of an electric faucet. Considering that the highest power model of the 220 V version of the Supreme faucet was inadvertently connected to a network with a nominal voltage of 127 V, and that the appliance is configured to work at its maximum power. What is the approximate value of the power when turning on the faucet?
06-(ENEM-MEC)
The electrical energy consumed in homes is measured in kilowatt-hours by means of a consumption meter. On this meter, from right to left, there are the hands of the units, tens, hundreds and thousands. If a hand is between two numbers, the last number passed by the hand is considered. Suppose that the measurements indicated in the following diagrams were made in a city where the price of the kilowatt-hour was R$ 0.20.
The amount to be paid for the registered electricity consumption would be
Exercises with ENEM characteristics
07 – (UFSM-RS)
One of the applications of X-rays is in observing the bones of the human body.
X-rays are produced when electrons emitted by a heated filament are accelerated by an electric field and strike a metal target at very high speed. If 1.0.10 18 electrons (e=1.6.10 -19 C) strike the target per second, the electric current in the tube, in A, is:
08-(UNIFESP-SP)
In an electricity book you will find three pieces of information: the first states that insulators are bodies that do not allow the passage of electric current; the second states that air is an insulator and the third
states that, on average, lightning consists of an electric discharge corresponding to a current of 10,000 amps that passes through the air and moves, from the cloud to the Earth, about 20 coulombs. It can be concluded that these three pieces of information are
a) coherent, and that the average time interval of an electric discharge is 0.002 .
b) coherent, and that the average time interval of an electric discharge is 2.0 s.
c) conflicting, and that the average time interval of an electric discharge is 0.002 s.
d) conflicting, and that the average time interval of an electric discharge is 2.0 s.
e) conflicting, and that it is not possible to evaluate the average time interval of an electric discharge.
09-(FUVEST-SP)
Electrical measurements indicate that the Earth’s surface has a total negative electrical charge of approximately 600,000 coulombs.
In thunderstorms, positively charged lightning bolts, although rare, can reach the Earth’s surface. The electric current from these bolts can reach values of up to 300,000 A. What fraction of the Earth’s electric charge could be offset by a 300,000 A lightning bolt lasting 0.5 s?
10- (UPE-PE)
The 0.3 A current passing through the chest can produce fibrillation (excessively fast contractions).
fast-acting muscle fibrils) in the heart of a human being, disturbing the rhythm of the heartbeat with possibly fatal effects. Assuming that the current lasts 2.0 min, the number of electrons that pass through the human being’s chest is — electron charge = 1.6 x10 -19 C
11-(UFPE-PE)
The graph shows the variation of the electric current I, in amps, in a wire as a function of time t, in seconds.
What is the electric charge, in coulombs, that passes through a cross section of the conductor in the first 4.0 seconds?
12-(UECE-CE)
A 12 V battery with a 60 Ah charge capacity powers a sound system, providing it with
system with a power of 60 W. Consider that the battery, at the beginning, is fully charged and will only power the sound system, so the battery voltage will remain at 12 V until the 60 Ah of charge is consumed. The maximum time of uninterrupted operation of the sound system in hours is:
13-(UFJF-MG)
The graph shows the electrical power, in kW, consumed in the residence of a resident of the city of Juiz de Fora, throughout the day. The residence is supplied with a voltage of 120 V. This residence
It has a circuit breaker that trips if the electrical current exceeds a certain value, to prevent damage to the electrical installation. On the other hand, this circuit breaker is sized to support a current used in the operation of all appliances in the residence, which adds up to a total power of 7.20 kW.
The maximum current value that the circuit breaker can support, the energy in kWh consumed throughout a day in this residence and the price to be paid for a month of consumption, if 1kWh costs R$ 0.50, are, respectively:
a) 20 A, 30kWh and R$360.00
b) 60 A, 24kWh and R$360.00
c) 24 A, 60kWh and R$240.00
d) 50 A, 12kWh and R$120.00
e) b) 60 A, 24kWh and R$240.00
14-(PUC-RJ)
Three-temperature electric showers are widely used in Brazil. To install a shower, you need to choose the power of the shower and the voltage that you will use in your electrical installation.
Therefore, if we install a 4,500 W shower using a 220 V voltage, we can use a circuit breaker that can handle the passage of 21 A. If we want to connect another 4,500 W shower to a 110 V voltage network, which circuit breaker should we choose?
15- (UNIFOR-CE)
Our energy matrix is predominantly of hydraulic origin. Our plants, such as Itaipú, Sobradinho, Paulo Afonso and Tucuruí, are located at great distances from the centers
energy consumers, making it necessary to transmit energy through extensive lines. The choice for this type of transmission, in high voltage and low intensity alternating current, occurs because:
I. The transmission of large power at low voltage and low current is economically viable.
II. High-intensity, low-voltage current transmission would require a large loss of power due to the heating of the transmission lines.
III. Alternating current transmission allows for simplified voltage reduction through transformers at step-down stations in consumer centers.
a) I, only.
b) II, only.
c) III, only.
d) I and III, only.
e) II and III, only.