Chapter 3: Electric Circuits

"What is an electric field?"

"The region around a charge where its effects can be felt; a force acts on another charge entering it."

"What are the two types of electric charge?"

"Positive and negative."

"What happens when a body has equal positive and negative charges?"

"It is neutral."

"What is the rule for charges interacting?"

"Like charges repel, opposite charges attract."

"In what direction do electric field lines point?"

"Away from positive charges, towards negative charges."

"What does the strength of an electric field depend on?"

"Strength of the charge and distance from the charge."

"What type of force is electrostatic force?"

"A non-contact force."

"What happens when two insulators are rubbed together?"

"Electrons are transferred, one becomes positive (loses electrons), the other negative (gains electrons)."

"Why do insulators become charged when rubbed?"

"Electrons cannot flow through them, so charge builds up."

"What is sparking?"

"When charge jumps through air between a highly negative and positive object."

"Why don't conductors become charged when rubbed?"

"Electrons flow in/out easily, cancelling effects."

"What is electric current?"

"The flow of electrical charge."

"What conditions are needed for current to flow?"

"A closed circuit and a source of potential difference."

"What is the equation for charge flow?"

"Q = It (Charge = current × time)."

"In a single closed loop

what is true about current?","It is the same at all points."

"What is the equation linking potential difference

current and resistance?","V = IR."

"What happens to current if resistance increases (for a fixed voltage)?"

"Current decreases."

"What is an ohmic conductor?"

"A component with constant resistance; current is directly proportional to potential difference."

"Why does a filament lamp's resistance increase with current?"

"Filament heats up, atoms vibrate more, collisions increase, making it harder for electrons to flow."

"How does a thermistor's resistance change with temperature?"

"Resistance decreases as temperature increases."

"How does an LDR's resistance change with light?"

"Resistance decreases as light intensity increases."

"What is the function of a diode?"

"Allows current to flow in one direction; very high resistance in the reverse direction."

"In a series circuit

how does current behave?","Same everywhere in the circuit."

"In a series circuit

how is potential difference distributed?","Shared across all components; total PD = sum of PD across each component."

"In a series circuit

how is resistance calculated?","Total resistance = sum of resistances of each component."

"In a parallel circuit

how does potential difference behave?","Same across all branches."

"In a parallel circuit

how does current behave?","Splits between branches; total current = sum of currents in each branch."

"In a parallel circuit

what is the total resistance compared to each branch?","Less than the resistance of the smallest branch."

"What is potential difference (definition)?"

"Work done per unit charge."

"What is the equation for potential difference in terms of work done and charge?"

"V = W / Q."

"What does power measure?"

"Rate of energy transfer or work done per second."

"What is the equation for power in terms of current and potential difference?"

"P = IV."

"Why does the National Grid use step-up transformers?"

"To increase potential difference and reduce current, minimising energy loss in transmission."

"What is the equation for power loss in cables?"

"P = I²R."

"How can power loss be reduced in transmission?"

"Use lower current (step up PD with transformers)."

"What direction do magnetic field lines go?"

"From north pole to south pole."

"What happens to magnetic field strength with distance?"

"Decreases with distance from magnet."

"What is a permanent magnet?"

"Always magnetic, with fixed poles."

"What is an induced magnet?"

"Becomes magnetic when placed in a magnetic field, loses magnetism when removed."

"Why does a compass point north?"

"Its needle aligns with Earth's magnetic field."

"Why is Earth's magnetic north pole actually a magnetic south pole?"

"Because the north pole of a compass is attracted to it, and opposite poles attract."

"What does a current-carrying wire produce?"

"A circular magnetic field around the wire."

"What is the right-hand grip rule?"

"Thumb = current direction, fingers curl = magnetic field direction."

"What factors affect the strength of a magnetic field around a wire?"

"Size of current and distance from wire."

"What is a solenoid?"

"A coil of wire that produces a strong magnetic field like a bar magnet when current flows."

"How can the strength of a solenoid be increased?"

"Increase current, add more turns, increase length, reduce cross-sectional area, use a soft iron core."

"How does a loudspeaker work?"

"A current-carrying coil interacts with a magnetic field, making the coil move, vibrating the cone to produce sound."

"What is the motor effect?"

"A force is exerted on a current-carrying conductor in a magnetic field due to interaction of fields."

"In what direction is the force in the motor effect?"

"At right angles to both the magnetic field and current."

"What rule is used to find the direction of force in the motor effect?"

"Fleming's Left-Hand Rule."

"What is the equation for force on a current-carrying conductor?"

"F = BIL (B = flux density, I = current, L = length)."

"How does an electric motor rotate?"

"Forces act on opposite sides of a current-carrying coil between magnets, making it spin."

"What is electromagnetic induction?"

"A potential difference is induced across a conductor when it moves relative to a magnetic field."

"When will a current flow in electromagnetic induction?"

"When the conductor forms a complete circuit."

"What is Lenz's Law (basic idea)?"

"The induced current creates a magnetic field that opposes the change producing it."

"How does an alternator work?"

"A coil rotates in a magnetic field, inducing an alternating current (AC)."

"How does a dynamo differ from an alternator?"

"Uses a split-ring commutator to produce direct current (DC)."

"How do transformers work?"

"AC in primary coil produces a changing magnetic field, inducing AC in secondary coil."

"What happens in a step-up transformer?"

"Secondary coil has more turns, increasing voltage."

"What happens in a step-down transformer?"

"Secondary coil has fewer turns, reducing voltage."

"What is the transformer equation?"

"Np / Ns = Vp / Vs = Is / Ip."

"Why don't transformers work with DC?"

"DC produces a constant magnetic field, no induction in the secondary coil."

"How does a dynamic microphone work?"

"Sound waves move a coil around a magnet, inducing a current proportional to the sound."