More On Resistance

?

Cells in Series

  • When cells are in series then the total emf is the sum of the emf of the cells
  • It makes no difference if there are components between the cells (including internal resistance)
  • The cells must be the same orientation in the circuit or the emf cancels out.
  • e(total) = e1 + e2 + ... + en
1 of 6

Resistance in Circuits

  • Resistance in series adds together in a circuit: Rtotal = R1 + R2 + ... + Rn
  • Knowing the total resistance of a circuit allows the current flow through a circuit to be calculated. Remember that the current in a simple series circuit is the same everywhere:
  • I = e[total] / R[total]
2 of 6

Celaculating PD across a resistor or component

  • Once you knoe (through measurement or calculation) the current flow in the circuit you can calculate the PD across the component:
  • V=IR
3 of 6

Cells in Parallel

  • The total current in the circuit is split between the cells equally so far n cells the current through each must be 1/n
  • The output pd measured across the cell is the emf minus the "lost" pd from the internal resistance
  • V = e - (Ir)n
4 of 6

Resistance in Parallel

  • Resistance in parallel is calculated by:
  • (1/Rtotal) = (1/R1) + (1/R2) + ... + (1/Rn)
  • For identical resistors in parallel, the quicker calculation is:
  • Rtotal = R / n
5 of 6

Diodes

  • Diodes are components that offer very high resistance in one direction so cuurent only passes one way
  • If it is not specified then assume a forward biased diode has a pf across it of 0.6V and infinite if reversed.
6 of 6

Comments

No comments have yet been made

Similar Physics resources:

See all Physics resources »See all Direct Current Circuits resources »