charge and current

• What does charge cause when placed in an electric field?

  It experiences an electrical force
• How is current defined in physics?

  Rate of flow of charge
• What is the formula for current?

  Current = change in charge / change in time
• What are the units for current, charge, and time?

  Amps, coulombs, seconds
• How can an amp be expressed in terms of charge?

  As coulombs per second
• What does it mean that charge is quantized?

  It comes in indivisible quantities
• What is the value of the elementary charge?

  Approximately $1.6 \times 10^{-19} \text{ coulombs}$
• What is the charge of an electron?

  Negative $1.6 \times 10^{-19} \text{ coulombs}$
• What is the charge of a proton?

  Positive $1.6 \times 10^{-19} \text{ coulombs}$
• How do you calculate the total charge on multiple electrons?

  Total charge = number of electrons × elementary charge
• If there are five electrons, what is the total charge?

  Approximately $8.0 \times 10^{-19} \text{ coulombs}$
• What are charge carriers in conductors?

  Free electrons
• What are charge carriers in electrolytes?

  Ions
• What happens to positive ions in a circuit?

  They move towards the positive terminal
• What happens to negative ions in a circuit?

  They move towards the negative terminal
• What is conventional current?

  Flow from positive to negative
• How does electron flow differ from conventional current?

  Electrons flow from negative to positive
• What does Kirchhoff's first law state?

  Sum of currents entering equals exiting
• What does Kirchhoff's first law represent?

  Conservation of charge
• If 5 amps and 2 amps enter a junction, what exits?

  7 amps
• What is number density?

  Charge carriers per unit volume
• What are the units of number density?

  Meters to the power of minus 3
• What is drift velocity?

  Average displacement per unit time of charge carriers
• What is the direction of drift velocity?

  Along the conductor
• What is the equation for drift velocity?

  $v =$$\frac{i}{n a e}$
• If the current is 0.03 amps, what is the drift velocity?

  Approximately $9.9 \times 10^{-4} \text{ m/s}$
• How does number density relate to conductivity?

  Higher number density means better conductivity
• What is the number density of insulators?

  Very low number density
• What is the number density of semiconductors?

  In between conductors and insulators
• What is the focus of the OCR Physics A specification?

  Charge and current
• Why is it important to understand charge and current?

  Fundamental concepts in physics and electronics
• What are the two main types of electrical circuits?

  Series circuit and parallel circuit
• What is a characteristic of a series circuit?

  It has only one path for current
• If the current in a series circuit is 0.1 amp, what is the current through each resistor?

  0.1 amp through each resistor
• How is voltage shared in a series circuit?

  Voltage is divided among components
• What is Kirchhoff's first law about currents at a junction?

  Sum of currents entering equals exiting
• What does Kirchhoff's second law state?

  Sum of emfs equals sum of potential differences
• If the emf in a series circuit is 5 volts, what is the potential difference across two identical resistors?

  2.5 volts across each resistor
• How does the presence of junctions affect current in a parallel circuit?

  Current splits at junctions in parallel
• What is generally true about potential difference in parallel circuits?

  Potential difference is the same across components