2c-Energy and voltage in circuits Flashcards
Q: Why is a series circuit more appropriate for some applications?
A:
In a series circuit, current is the same everywhere.
Voltage is shared between components.
Used in:
Fairy lights (if one bulb blows, the whole circuit stops working).
Low-power devices where equal current is needed.
Q: Why is a parallel circuit more appropriate for domestic lighting?
Voltage across each branch is the same, so all bulbs get full mains voltage.
If one bulb fails, others continue to work.
Used in:
House lighting circuits.
Car headlights (both stay bright independently).
Q: How does current behave in a series circuit?
A:
Current is the same at all points in a series circuit.
It does not split, as there is only one path for electrons to flow.
The current depends on total resistance and applied voltage, following Ohm’s Law
I=V/ Rtotal
Q: How does current vary with voltage in different components?
A:
-Ohmic conductors (e.g., wires, resistors):
Follow Ohm’s Law:
V=I×R.
Current is directly proportional to voltage, producing a straight-line graph.
-Filament lamps:As voltage increases, temperature increases, causing resistance to increase.
The current increases at a decreasing rate, producing a curved
I−V graph.
-Diodes and LEDs:Allow current to flow only in one direction.
In the forward direction, there is almost no current until a threshold voltage is reached, then it rises rapidly.
In the reverse direction, resistance is very high, and no current flows.
-Investigating experimentally:Use a variable power supply, ammeter, and voltmeter to measure current and voltage.
Plot an I-V graph to observe relationships for different components.
Q: How can you investigate how current varies with voltage experimentally?
A:
Set up a circuit with:
Ammeter (series) to measure current.
Voltmeter (parallel) to measure voltage.
Variable power supply and the component under test.
Increase voltage gradually and record current readings.
Plot an I-V graph to analyze:
Resistor → Straight line (Ohm’s Law).
Filament lamp → Curved graph (resistance increases with temperature).
Diode → No current until a threshold voltage is reached.
Conclusion: Current depends on voltage and component resistance.
Q: What is the effect of resistance on current?
A:
Higher resistance → Lower current (Ohm’s Law:
𝐼
=
𝑉
𝑅
I=
R
V
).
Lower resistance → Higher current.
Example:
Adding resistors in series increases resistance, reducing current.
Adding resistors in parallel decreases total resistance, increasing current.
Q: How does the resistance of LDRs and thermistors change?
A:
1: LDR (Light-Dependent Resistor):
More light → Lower resistance (higher current).
Less light → Higher resistance (lower current).
Used in: Streetlights, automatic night lights.
2: Thermistor:
Higher temperature → Lower resistance (higher current).
Lower temperature → Higher resistance (lower current).
Used in: Temperature sensors, thermostats.
Q: How can lamps and LEDs be used to detect a current?
A:
A lamp lights up when a current flows.
An LED (Light Emitting Diode) glows only when current flows in one direction.
Used in: Indicator lights, electronic circuits.
Q: What is electric current?
A:
The rate of flow of charge.
Formula:
Q=I×t
(Charge = Current × Time).
Measured in amperes (A).
In metallic conductors, current is the flow of negatively charged electrons.
Conventional current flows from positive to negative, but electron flow is from negative to positive..
Q: What is the nature of electric current in metals?
A:
Current in metals is the flow of negatively charged electrons.
Electrons move from negative to positive in the circuit.
Q: Why is current conserved at a junction in a circuit?
A:
Total current entering a junction = Total current leaving the junction.
Example: If 3A enters and splits into two branches, one might carry 1A, the other 2A.
Q: What happens to voltage in a parallel circuit?
A:
Voltage across all branches is the same.
Example: If mains voltage is 230V, each parallel branch also gets 230V.
Q: How can you calculate current, voltage, and resistance in a series circuit?
A:
Current is the same throughout the circuit.
Total resistance is the sum of all resistances:
𝑅
total
=
𝑅
1
+
𝑅
2
R
total
=R
1
+R
2
Use Ohm’s Law to calculate unknown values.
: What does voltage represent in a circuit?
A:
Voltage = Energy transferred per unit charge.
1 volt = 1 joule per coulomb.
How Does Current Vary with Voltage in Different Components?
Ohmic Conductors
Ohmic Conductors (e.g., wires, resistors):
Follow Ohm’s Law:
V=I×R.
Current is directly proportional to voltage, producing a straight-line
I−V graph.
How Does Current Vary with Voltage in Different Components?
Filamnet lamps
Filament Lamps:
As voltage increases, temperature increases, causing resistance to increase.
Current increases at a decreasing rate, producing a curved
𝐼
−
𝑉
I−V graph.
How Does Current Vary with Voltage in Different Components?
Diodes& LEDs
Diodes & LEDs:
Allow current in only one direction.
No significant current until a threshold voltage is reached, then it rises rapidly.
In the reverse direction, resistance is very high, and no current flows.
How Does Current Vary with Voltage in Different Components?
Experimental investorigation
Experimental Investigation:
Use a variable power supply, ammeter, and voltmeter.
Record current for different voltages and plot an I-V graph to analyze the relationship.
