24.4
Potencial Elétrico e Diferença de Potencial
Suponha que uma carga de teste positiva se afasta de uma carga estática positiva, então a força de Coulomb realiza trabalho positivo e sua energia pot…
Considere um campo elétrico estático produzido por uma carga pontual positiva. Se uma carga de teste positiva se mover nele, o trabalho realizado na carga é uma mudança negativa na energia potencial elétrica.
Dividindo a equação de trabalho acima pela carga total em uma carga de teste, obtém-se a diferença de potencial elétrico.
A diferença de potencial elétrico é igual à quantidade de trabalho realizado para mover uma carga unitária do ponto inicial para o final.
O potencial elétrico é a energia potencial elétrica por unidade de carga. É uma grandeza escalar com a unidade SI de volts (joules por coulomb).
Em circuitos eletrônicos, uma diferença de potencial entre dois pontos é chamada de tensão, que é medida por um voltímetro.
A expressão para potencial devido a uma única carga pontual pode ser generalizada para uma coleção de cargas pontuais tomando a soma algébrica do potencial devido às cargas individuais.
No caso de uma distribuição de carga contínua, o potencial é calculado usando a integral dos elementos de carga na distância em que o potencial elétrico é calculado.
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Q1: What is the difference between electric potential and electric potential energy?
Electric potential energy is the total energy stored due to a charge's position in an electric field. Electric potential is the electric potential energy per unit charge, making it independent of the test charge itself. While potential energy depends on the charge magnitude, potential does not. Both are scalar quantities measured in joules and volts respectively.
Q2: How is electric potential difference defined and measured?
Electric potential difference is the ratio of change in potential energy to the test charge moved between two positions. It equals the work done per unit charge to move a charge from one point to another. Measured in volts (joules per coulomb), potential difference is also called voltage in electronic circuits and is measured using a voltmeter.
Q3: Why do batteries with the same voltage store different amounts of energy?
Voltage represents energy per unit charge, not total energy. A 12-volt motorcycle battery and a 12-volt car battery have identical potential differences between terminals, but the car battery can move more total charge. Since energy equals voltage multiplied by charge, the car battery stores more total energy despite having the same voltage.
Q4: How is electric potential calculated for multiple charges?
For multiple point charges, electric potential is found by taking the algebraic sum of potentials from individual charges. For continuous charge distributions, the potential is calculated by integrating charge elements over the distance where potential is measured. This superposition principle allows complex charge configurations to be analyzed systematically.
Q5: What happens to electric potential energy when a positive charge moves away from another positive charge?
When a positive test charge moves away from a positive static charge, the Coulomb force does positive work on it. This positive work results in a decrease in electric potential energy. The electric potential at that location also decreases as distance from the source charge increases.
Q6: What are the SI units for electric potential and potential difference?
Electric potential and potential difference are measured in volts (V), named after Alessandro Volta. One volt equals one joule per coulomb, representing the energy per unit charge. This unit is fundamental in electronics and physics, appearing on voltmeters and battery labels worldwide.
Q7: How does electric potential relate to work done on a test charge?
Electric potential difference equals the work done per unit charge to move a test charge between two points. When a positive charge moves in a static electric field, the work done on it represents a change in potential energy. Dividing this work by the test charge magnitude yields the potential difference between those positions.