Chapter 2 - Sensing Flashcards
Why do cells and batteries warm up when used?
Due to internal resistance
Why does resistance occur?
Electrons collide with atoms and lose energy
What is the load resistance?
Total resistance of all components in the external circuit.
When could the terminal p.d be the same as the e.m.f?
When there is no internal resistance
The potential difference in the external circuit is called the
Terminal p.d
E.m.f formula
V = ε - Ir
E.m.f equation
ε = I (R + r)
What does the emf equation state in terms of voltage
ε = V + v
When would it be useful to have a large internal resistance?
In high voltage power supplies to prevent short circuiting danger as only small current would flow
What does the conservation of charge tell us?
The total current entering a junction = the total current leaving it
I1 = I2 + I3
What does the conservation of energy in circuits indicate?
The total e.m.f around a series circuit = sum of p.d.s across each component
Key points about a series circuit
- Same current at all points (as there are no junctions)
- E.m.f is split between components
- R total = R1 + R2 + R3
Key points of a parallel circuit
- Current is split at each junction
- Same p.d across all components (separate loops in which e.m.f = sum of individual p.d.s)
- G total = G1 + G2 + G3
1/R total = 1/R1 + 1/R2 + 1/R3
How does an LDR function?
Very high resistance in the dark
Low resistance in the light
How does a thermistor function?
High resistance at low temperatures
Low resistance at high temperatures
