Electricity Flashcards
What are the two types of electric charges?
Positive charge (+) and Negative charge (–)
What is the law of attraction and repulsion for charges?
Like charges repel, unlike charges attract.
How can an object be classified based on its charge?
- Positively charged: more (+) than (–)
- Negatively charged: more (–) than (+)
- Neutral: equal number of (+) and (–)
What are good conductors and why?
Metals, because they contain a large number of freely moving electrons allowing charge to pass.
What are insulators and why?
Rubber, wood, plastic, because they contain few freely moving electrons and don’t allow charge to pass.
How can an insulator be charged?
By rubbing, transferring electrons between the objects.
Why must the cloth be dry when charging an insulator by rubbing?
Water is a conductor and would prevent effective charge transfer.
How can a conductor be charged by induction?
By bringing a charged rod close, allowing electrons to move, then grounding and removing the charge source.
What is an electric field?
The region surrounding a charge where an electric force is exerted.
What do electric field lines represent?
The direction and strength of the electric field; they originate from positive charges and enter negative charges.
What does a battery do in a circuit?
Converts chemical energy into electrical energy.
What is the voltage of a single cell?
1.5V
What is the function of a bulb in a circuit?
Acts as an indicator for electric current.
What is the function of a switch?
Controls the flow of current, typically drawn in an open position.
What is an ammeter used for, and how is it connected?
Measures current (A) and must be connected in series.
How is electric current defined and calculated?
The amount of charge passing per second:
𝐼 = 𝑄 / 𝑡
What is conventional current direction?
From the positive terminal of the battery to the negative terminal.
What is the function of a voltmeter and how is it connected?
Measures voltage (V) and must be connected in parallel.
What is Ohm’s Law?
V = IR
How is resistance calculated?
R = V / I
What happens to total resistance in a series circuit?
It increases:
𝑅(𝑇) = 𝑅(1) + 𝑅(2) + 𝑅(3)
What are disadvantages of series circuits?
If one component fails, all fail; brightness of bulbs decreases.
How is total resistance calculated in a parallel circuit? (for two resistors)
𝑅(𝑇) = (𝑅[1] x 𝑅[2]) / (𝑅[1] + 𝑅[2])
multiply / add
What are advantages of parallel circuits?
If one component fails, others work; bulbs maintain same brightness.
How does wire length affect resistance?
Longer wires have higher resistance.
How does cross-sectional area affect resistance?
Greater area results in lower resistance.
How does temperature affect resistance in metals?
Higher temperature increases resistance due to more collisions between electrons and the lattice.
How does temperature affect resistance in semiconductors?
Higher temperature decreases resistance.
What is the formula for resistance of a wire?
R = (ρxL) / A
What analogy explains current, voltage, and resistance?
- Current: Delivery crew carrying sandwiches
- Voltage: Energy sandwiches from battery to components
- Resistance: Traffic affecting crew’s movement
What is a rheostat?
A variable resistor used to control current.
What is a thermistor and how does it work?
A temperature-dependent resistor; lower resistance at high temperatures.
What is an LDR (Light-Dependent Resistor)?
A resistor that decreases in resistance when exposed to light.
What is a diode and how does it function?
A semiconductor that allows current to pass in one direction.
What happens when a diode is forward-biased? (connected forward)
It has low resistance and allows current to pass.
What happens when a diode is reverse-biased? (connected in reverse)
It has high resistance and blocks current.
What is an LED (Light Emitting Diode)?
A diode that emits light when forward-biased.
What are the three wires in a European plug?
- Live wire (carries electricity) [Blue]
- Neutral wire (closes circuit) [Brown]
- Earth wire (prevents shocks) [Yellow/Green]
What is a circuit breaker and how does it work?
A safety device that shuts down power when excessive current generates a strong magnetic field.
How does a fuse protect a circuit?
It melts when excessive current passes, breaking the circuit.
What are fuse ratings?
The fuse must be slightly larger than the normal operating current.
What is double insulation?
The outer case of a device is made of an insulator to prevent electric shocks.
What is a potential divider?
A circuit that divides voltage based on resistor values.
What happens in a variable resistor with a sliding contact?
Moving the slider changes the length, resistance, and voltage.
What is the difference between direct and alternating current?
- DC (Direct Current): Flows in one direction (batteries).
- AC (Alternating Current): Changes direction periodically (generators).
How do you charge a conductor negatively by induction?
To charge negatively by induction, bring a positively charged rod near a neutral conductor so that electrons in the conductor are attracted toward the rod. While the rod is in place, connect the conductor to ground; electrons will flow from the ground into the conductor, giving it a net negative charge. Then remove the ground connection and finally remove the rod.
Why does the V–I graph of a filament lamp deviate from a straight line?
- As current flows through a filament, it heats up, causing its temperature to increase.
- As temperature increases lattice of material vibrates more and collides more with electrons, therefore current decreases and resistance increases.
- This rising resistance results in a non-linear (curved or plateauing) V–I graph rather than a straight line as predicted by Ohm’s law for constant resistance.
What factors determine the resistance of a wire, and what is the governing formula?
The resistance of a wire depends on its material’s resistivity (ρ), its length (l), and its cross-sectional area (A). The formula is:
* 𝑅 = (𝜌 × 𝑙) / 𝐴
How do electric field lines indicate both the direction and strength of an electric field?
Electric field lines start from positive charges and end on negative charges. Their direction shows the field’s direction, and the closer the lines are to each other, the stronger the field at that region.
How does a potential divider work in a series circuit?
In a potential divider, the voltage drop across each resistor is proportional to its resistance. By adjusting the resistor values (or moving a slider on a resistance wire), you obtain a desired fraction of the total voltage.
What are the proper ways to connect an ammeter and a voltmeter in a circuit?
An ammeter is connected in series to measure the current flowing through the circuit, whereas a voltmeter is connected in parallel across a component to measure the voltage drop.
What are the key differences between alternating current (AC) and direct current (DC)?
- DC flows in one constant direction (typical of batteries)
- AC periodically reverses direction and its magnitude varies with time (typical of generators)
How does a diode function in forward and reverse bias?
- In forward bias, a diode has low resistance and allows current to pass
- In reverse bias, it exhibits high resistance and blocks current flow.
- This property is used, for example, in converting AC to DC.
