17 — D.c. circuits Flashcards
Series circuit
A series circuit is a connection where the components are connected one after another in a single loop and there is only one path through which electric current can flow
Current: same
Pd: sum
Achieves higher effective resistance than parallel arrangement
Bulb usually less bright than parallel
Parallel circuit
A parallel circuit is a connection where there is more than 1 path through which electric current can flow
Bulb usually brighter than n series cus volt identical
Current splits across diff parallel branches -> current thru each cell = V/R -> when more parallel branches added, current is overdrawn from power source -> power depletes quickly
Transducers
Are electrical devices that convert energy from one form to another
Eg thermistors, light-dependent resistors, photovoltaic cells and piezoelectric sensors
Thermistors
Device which resistance varies with temperature
LDRs
A device whose resistance varies with the amount of light shining on it
Light intensity increases, resistance decreases
Define potential divider
A potential divider is a a line of resistors connected in series, it is used to provide a fraction of the voltage of a source to another part of the circuit.
Explain why the pd across lamp is not proportional to the current in it
The lamp is a non-ohmic conductor. The lamp’s resistance increases as the tempt increases, resulting in pd across lamp not proportional to current.
Explain how the student gradually increases the current in the lamp form zero using potentiometer.
By moving the jockey of the potentiometer from Q to P, potential diff across bulb would increase from 0V to 12V thus current increases from 0V.
Explain why the brightness of lamp increases when the light source is placed next to LDR and the thermistor is heated.
- Potentiometer method
As LI increases, resistance of LDR decreases -> pd of LDR decreases. As tempt increases, resistance of thermistor decreases -> pd of thermistor decreases -> pd across bulb increases -> bulb brighter. - Current in a series circuit method
As LI increases, resistance of LDR decreases -> pd of LDR decreases. As tempt increases, resistance of thermistor decreases. Since total effective resistance decreases, by V=IR, pd increases, brightness increases.
Describe and explain how the brightness of bulb changes when env brightness decreases.
Under dim lighting, resistance of a LDR increases and since it is connected in parallel to a fixed resistor, total resistance will increase. From potential divider concept, the pd across the combined setup or bulb will increase which also increase its brightness.
Explain why the voltmeter reading increases as tempt rises
When tempt increases, resistance of thermistor decreases. The pd across thermistor decreases thus pd across the fixed resistor will increase by V=R1/R1+R2 X V0. Therefore, the voltmeter will register an increase in reading.
Parallel circuit. Filament of one of the bulb breaks. Comment on wut happens to the ammeter reading and brightness of the bulb.
Ammeter reading decreases since total effective resistance of circuit increases.
The brightness of the bulb remains the same as the pd of the bulbs in parallel branches remains the same. Assuming resistance remains constant, the current in each branch will also remain the same. Hence, brightness remains the same.
State why the pd across the 2 fixed resistors r the same
Since both resistors have the same resistance of x ohm, the emf is shared equally among the 2 resistors.
State an advantage of using a potential divider circuit than a series circuit to control the brightness of the lamp.
Both circuits can control the brightness of the lamp. However, a potential meter circuit may short-circuit the lamp and therefore switch off the lamp, which a series circuit cannot achieve.
Explain why when a much higher resistance resistor is used in a series circuit, the life of the battery increases.
Replacing R with a larger resistance resistor increases the effective resistance of the circuit. This results in a lower current in the battery. Therefore, the power loss in the battery is decreased and hence has a longer lifespan.
