Define electric current, voltage, and resistance in terms of electron flow and energy.
A circuit has a voltage of $230~\mathrm{V}$ (typical European mains) and a current of $1.75~\mathrm{A}$ flowing through it.
a) Calculate the resistance in the circuit.
b) Explain why doubling the voltage would double the current.
A $470~\Omega$ resistor is connected to a $9.00~\mathrm{V}$ battery (common for electronics).
a) What is the current flowing through the circuit?
b) If the resistor is replaced with a $1.00~\mathrm{k}\Omega$ resistor, how does the current change?
A microwave oven draws $12.5~\mathrm{A}$ of current when connected to a $120~\mathrm{V}$ outlet (typical US mains). What is its resistance?
An LED has a resistance of $33.0~\Omega$ and requires $15.0~\mathrm{mA}$ to operate.
a) What voltage must be applied across the LED?
b) Why is the direction of current flow important for LEDs?
A battery supplies $24.0~\mathrm{V}$ to a circuit with two identical resistors. If the total current is $0.800~\mathrm{A}$, what is the resistance of each resistor?
A car battery provides $12.6~\mathrm{V}$. If a car starter motor draws $185~\mathrm{A}$ during starting:
a) Calculate the resistance of the starter motor.
b) How much charge flows through it in $3.00~\mathrm{s}$?
A laptop charger supplies $19.5~\mathrm{V}$ and $3.33~\mathrm{A}$ to charge in 2.00 hours.
a) What is the effective resistance of the charging circuit?
b) How much charge is transferred in the $2.00~\mathrm{hours}$?
a) $R = 131~\Omega$
b) Doubling voltage doubles current when resistance is constant (Ohm’s Law)
a) $I = 0.0191~\mathrm{A}$
b) $I = 0.00900~\mathrm{A}$
$R = 9.60~\Omega$
a) $V = 0.495~\mathrm{V}$
b) LEDs are diodes that only conduct in one direction
If series: $R_{each} = 15.0~\Omega$ If parallel: $R_{each} = 60.0~\Omega$
a) $R = 0.0681~\Omega$
b) $Q = 555~\mathrm{C}$
a) $R = 5.86~\Omega$
b) $Q = 24000~\mathrm{C}$