Física - Eletricidade Practice Questions
ENEM (Brazil) · ENEM Ciências da Natureza · 138 free MCQs with instant results and detailed explanations.
138
Total
35
Easy
75
Medium
28
Hard
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Sample Questions from Física - Eletricidade
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Q1
Easy
If a circuit contains a 12V battery and a resistor of 4Ω, what is the current flowing through the circuit?
A.
3 A
B.
6 A
C.
12 A
D.
24 A
Show Answer & Explanation
Correct Answer: A
Using Ohm's law (V = IR), where V is voltage, I is current, and R is resistance, we can calculate current as I = V/R = 12V/4Ω = 3A.
Q2
Easy
Which of the following statements correctly describes a series circuit?
A.
Current is the same through all components.
B.
Voltage across each component is the same.
C.
Total resistance decreases as more components are added.
D.
Devices can be turned on or off independently.
Show Answer & Explanation
Correct Answer: A
In a series circuit, the current remains constant through all components; however, the voltage divides among the components, and total resistance increases with more components.
Q3
Easy
What is the primary reason a rubber balloon can be charged by rubbing it against a wool sweater?
A.
Electrons are transferred from the sweater to the balloon.
B.
Protons are transferred from the balloon to the sweater.
C.
The wool generates heat, causing the balloon to charge.
D.
The rubber absorbs positive charges from the sweater.
Show Answer & Explanation
Correct Answer: A
Rubbing the rubber balloon against the wool sweater transfers electrons from the sweater to the balloon, giving it a negative charge.
Q4
Medium
What is the main purpose of a transformer in electrical systems?
A.
To convert AC to DC
B.
To increase or decrease voltage levels
C.
To store electrical energy
D.
To measure electrical current
Show Answer & Explanation
Correct Answer: B
A transformer is specifically designed to increase or decrease voltage levels in an electrical system through electromagnetic induction, making option B the correct answer.
Q5
Medium
If a circuit has a total resistance of 30 ohms and a current of 2 amperes flowing through it, what is the voltage across the circuit?
A.
15 volts
B.
60 volts
C.
30 volts
D.
20 volts
Show Answer & Explanation
Correct Answer: B
Using Ohm's Law (V = I × R), we can calculate the voltage: V = 2 A × 30 Ω = 60 V, thus option B is the correct answer.
Q6
Medium
In a parallel circuit with three resistors of 12 ohms, 24 ohms, and 36 ohms, what is the total resistance of the circuit?
A.
8 ohms
B.
12 ohms
C.
18 ohms
D.
72 ohms
Show Answer & Explanation
Correct Answer: A
The total resistance in a parallel circuit is given by 1/R_total = 1/R1 + 1/R2 + 1/R3. Calculating, we get 1/R_total = 1/12 + 1/24 + 1/36, which simplifies to 1/R_total = 1/8, thus R_total = 8 ohms.
Q7
Medium
What happens to the resistance of a conductor if its length is doubled, while keeping the cross-sectional area constant?
A.
Resistance doubles
B.
Resistance halves
C.
Resistance remains the same
D.
Resistance quadruples
Show Answer & Explanation
Correct Answer: A
According to the formula for resistance R = ρ(L/A), if the length (L) is doubled while the area (A) remains constant, the resistance (R) also doubles.
Q8
Hard
A capacitor in an RC circuit is charged to a voltage of 12V. If the resistance in the circuit is 4Ω and the capacitance is 2F, what is the time constant of the circuit?
A.
8 seconds
B.
6 seconds
C.
4 seconds
D.
2 seconds
Show Answer & Explanation
Correct Answer: A
The time constant (τ) of an RC circuit is calculated using the formula τ = R * C. Here, R = 4Ω and C = 2F, so τ = 4 * 2 = 8 seconds.
Q9
Hard
In a parallel circuit, three resistors of values 6Ω, 12Ω, and 18Ω are connected. What is the equivalent resistance of the circuit?
A.
3Ω
B.
4Ω
C.
5Ω
D.
6Ω
Show Answer & Explanation
Correct Answer: A
The equivalent resistance (R_eq) in a parallel circuit is given by 1/R_eq = 1/R1 + 1/R2 + 1/R3. For R1 = 6Ω, R2 = 12Ω, R3 = 18Ω, we have 1/R_eq = 1/6 + 1/12 + 1/18, which simplifies to R_eq = 3Ω.
Q10
Hard
A parallel plate capacitor has a capacitance of 10 microfarads and is connected to a 50 V battery. How much energy is stored in the capacitor?
A.
0.025 J
B.
0.05 J
C.
0.1 J
D.
0.2 J
Show Answer & Explanation
Correct Answer: A
The energy (E) stored in a capacitor is given by the formula E = 0.5 * C * V^2. Substituting the values: E = 0.5 * 10e-6 F * (50 V)^2 = 0.025 J.
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Física - Eletricidade — ENEM (Brazil) ENEM Ciências da Natureza Practice Questions Online
This page contains 138 practice MCQs for the chapter Física - Eletricidade in ENEM (Brazil) ENEM Ciências da Natureza. The questions are organized by difficulty — 35 easy, 75 medium, 28 hard — so you can choose the right level for your preparation.
Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit.