Static & Charge (OCR GCSE Physics A (Gateway)): Flashcards
Exam code: J249
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What is charging by friction?
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What is charging by friction?
Charging by friction is the process of making an insulating material electrically charged by rubbing it against another insulating material.
True or False?
When an acetate rod is rubbed with a cloth, positive charges move from the cloth to the rod.
False.
It is electrons (negative charges) that are transferred — not positive charges. The rod loses electrons and becomes positively charged; the cloth gains electrons and becomes negatively charged.
When two insulating materials are rubbed together, .......... are transferred from one material to the other by friction.
When two insulating materials are rubbed together, electrons are transferred from one material to the other by friction.
Why does rubbing a rod with a cloth make the rod positively charged?
Rubbing transfers electrons from the rod to the cloth. Because electrons are negatively charged, the rod is left with more positive charges than negative, making it positively charged.
What is an electrically neutral object?
An electrically neutral object has equal numbers of positive and negative charges, giving an overall charge of zero.
An object becomes negatively charged when it .......... electrons and positively charged when it .......... electrons.
An object becomes negatively charged when it gains electrons and positively charged when it loses electrons.
True or False?
Both the rod and the cloth must be made of insulating materials for charging by friction to work.
True.
Charging by friction requires insulating materials because the charges remain on insulators — they cannot flow away as they would in a conductor.
What happens to the cloth when a rod is rubbed with it and loses electrons?
The cloth gains the electrons that left the rod, giving it an equal negative charge. The rod and cloth end up with opposite charges of the same magnitude.
What is a non-contact force?
A non-contact force is a force that acts on an object without physically touching it. The attraction and repulsion between charged objects are examples of non-contact forces.
True or False?
Two negatively charged objects placed near each other will attract.
False.
Objects with the same charge repel each other. Only objects with opposite charges attract.
Why does a negatively charged comb attract small pieces of paper?
The comb's negative charge draws the positive charges in the neutral paper to its surface. Because opposite charges attract, the paper sticks to the comb through static electricity.
An object gains a negative charge by .......... electrons and gains a positive charge by .......... electrons.
An object gains a negative charge by gaining electrons and gains a positive charge by losing electrons.
What is a static electricity spark?
A static electricity spark occurs when a large surplus of electrons causes charge to jump between two objects, creating a brief current. This can happen when touching a door handle after walking on a nylon carpet.
True or False?
Lightning is caused by the build-up of charge in storm clouds, which then discharges to the ground as a giant spark.
True.
Moving storm clouds transfer electrons between them, building up charge. Negative charges then jump to meet positive charges on the ground, forming lightning.
Explain why a balloon sticks to a wall after being rubbed on a woollen jumper.
Rubbing transfers electrons onto the balloon, making it negatively charged. The balloon's negative charge attracts the positive charges in the neutral wall to its surface, and the electrostatic attraction holds the balloon in place.
Opposite charges .......... while like charges ...........
Opposite charges attract while like charges repel.
Why can static sparks be dangerous near petrol?
A static spark is a brief flow of electrons between two charged objects. Near petrol, this spark can ignite the flammable vapour, causing a fire or explosion.
What is an electric field?
An electric field is a region where an electric charge experiences a force. It is created by a charged object and can attract or repel other charges that enter it.
True or False?
Electric field lines always point towards positive charges and away from negative charges.
False.
Field lines always point away from positive charges and towards negative charges.
How does distance affect the electric force between two charged objects?
The electric force becomes stronger as the objects move closer together and weaker as they move further apart. This applies to both attraction and repulsion.
The electric field between two parallel plates is a .......... field, with field lines directed from the .......... plate to the .......... plate.
The electric field between two parallel plates is a uniform field, with field lines directed from the positive plate to the negative plate.
What is a uniform electric field?
A uniform electric field is one where the field strength is the same at every point. It is produced between two parallel plates and is shown by evenly spaced, parallel field lines.
True or False?
Closer field lines indicate a stronger electric field.
True.
The strength of an electric field is shown by the spacing of its field lines. Lines that are closer together represent a stronger field.
What determines whether the electric force on a charge is attractive or repulsive?
It depends on the sign of the charges. Opposite charges (positive and negative) attract each other; same charges (both positive or both negative) repel each other.
Describe the shape of the electric field lines around a single positive point charge.
The field lines are radial — they spread outward in all directions from the positive charge, like the spokes of a wheel, pointing away from it.
Define electric current.
Electric current is the rate of flow of charge — the amount of charge passing through a component per second. In metal wires, current is a flow of electrons.
True or False?
An ammeter should always be connected in parallel with the component you want to measure.
False.
An ammeter must always be connected in series with the component, so that all the current flowing through it also flows through the ammeter.
Electric current is calculated using the equation: current = charge ÷ .......... and is measured in ..........
Electric current is calculated using the equation: current = charge ÷ time and is measured in amperes (A).
A charge of 6 C passes through a resistor in 2 s. Calculate the current. (Higher Tier Only)
Using I = Q ÷ t:
I = 6 ÷ 2
I = 3 A
Define conventional current.
Conventional current is defined as the flow of positive charge from the positive terminal to the negative terminal of a cell. This is the opposite direction to the flow of electrons.
True or False?
In a closed-loop (series) circuit, the current has the same value at every point in the loop.
True.
In a closed-loop circuit, the same number of electrons per second passes through every point, so the current is the same throughout.
What happens to the current at a junction in a circuit?
At a junction, current is conserved — the total current flowing into the junction equals the total current flowing out. This is because charge cannot be created or destroyed.
For a current to flow in a circuit, the circuit must include a source of .......... and must be .......... with no gaps.
For a current to flow in a circuit, the circuit must include a source of potential difference and must be closed with no gaps.
Why are metal wires used in electric circuits?
Metals are good conductors of electric current because they contain free electrons that can move easily through the metal, allowing charge to flow.
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