# 5 Direct current circuits

This section is about applying some more advanced rules to circuits that build on your GCSE skills. The trick is to realise that you must be 100% logical and treat it as a mathematical exercise. If you set up the problems correctly then you cannot go wrong. Take note of these things that you must be able to do…

1. Make sure you treat current and pd as having a direction.
2. Learn how to apply reciprocal equations for 1/R for resistors in parallel
3. Learn what the gradient and intercept mean on an Internal Resistance circuit graph
4. Remember that a power source is a “real source” and will get warm so lose energy! A 3V cell does not output 3V!
5. When thinking about potential dividers the trick is to realise that current is the same through each resistor. So setup two equations for V for each then I is the same for both!

AS Physics Unit 1_5 (Main PDF notes)

5.1 Circuit rules

5_1_kirchoffs laws (problem sheet)

5.2 More about resistance

5_2_Practical_investigating_resistors (Practical on Resistors)

5_2_practical_cons_energy (Practical sheet proving Kirchhoff’s laws)

resistor_cube_problem (Extension – 3D resistor cube problem – for fun!)

5.3 Emf and internal resistance

Internal Resistance Calculator (Hyper Physics)

5_3_EHT_Practical_Demo (teacher demo with results to graph)

5_3_Internal_Resistance Problems (probkems sheet)

5_3_IR_of_Battery variable current method (practical method 1)

5_3_IR_of_Cell adding bulbs method (practical method 2)   Results 3 Cells (excel results)

5_3_IR_Practical_Higher_Ability

5_3_IOP_notes  (extra reading from IOP)

5.4 More circuit calculations

5_4_Investigation_cell_combinations (Crucial practical which explores how PD behaves for series & parallel)

5.5 The potential divider

5_4_Potential_Dividers Worksheet

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