Ohm's Law

1. Definition of Ohm's Law

• Ohm's Law states that the potential difference (voltage) across a conductor is directly proportional to the current flowing through it, provided temperature remains constant.

• Formula: where: $R = \frac{V}{I}$

  • $R =$ Resistance $(Ω)$
  • $V =$ Potential difference $(V)$
  • $I =$ Current $(A)$

2. Definition of the Ohm

• A conductor has a resistance of 1 ohm $(Ω)$ if a potential difference of 1 volt $(V)$ across it causes a current of 1 ampere $(A)$ to flow through it.

3. Circuit Connections

a) Series Circuits

✔ Resistors are connected end to end → forms one path for current.

✔ Total resistance increases when resistors are added:

$R_{\text{total}} = R_1 + R_2 + R_3$

✔ Current remains the same throughout the circuit:

$I_{\text{total}} = I_1 = I_2 = I_3$

✔ Voltage divides across components:

$V_{\text{total}} = V_1 + V_2 + V_3$

b) Parallel Circuits

✔ Resistors are connected in branches → current splits into multiple paths.

✔ Total resistance decreases when more resistors are added:

$\frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$

✔ Total current is the sum of branch currents:

$I_{\text{total}} = I_1 + I_2 + I_3$

✔ Voltage remains the same across all parallel branches:

$V_{\text{total}} = V_1 = V_2 = V_3$

4. Key Takeaways

✔ Ohm's Law shows the relationship between voltage, current, and resistance.

✔ Series circuits increase resistance; parallel circuits decrease resistance.

✔ Voltage divides in series but stays the same in parallel.

Exam Tip

💡 For parallel circuits, always use the reciprocal formula when calculating total resistance!