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Physics 11
| Question | Answer |
|---|---|
| What are the two types of electric charge, what is the SI unit, and how do like/opposite charges interact? | Positive and negative charges; SI unit is the coulomb (C). Like charges repel, opposite charges attract. The electrostatic force weakens as distance between charges increases. |
| What is the difference between static electricity and polarization? | Static electricity is the buildup of charge on an object caused by charge transfer between materials (e.g., rubbing a balloon on hair). Polarization is a redistribution of existing charges within a neutral object — no transfer. |
| Define conductors, insulators, and superconductors. | Conductors (e.g., metals) allow electrons to move freely. Insulators (e.g., wood, rubber) restrict electron flow. Superconductors allow charge movement with zero energy loss. |
| State the Law of Conservation of Electric Charge. | The total electric charge in an isolated system remains constant. Charge cannot be created or destroyed — only transferred. If one part of a closed system loses charge, another part gains an equal amount. |
| What subatomic particles carry charge, and what is the elementary charge? | Protons (+) and electrons (−) each carry 1.60 × 10⁻¹⁹ C, called the elementary charge (e). Neutrons are neutral. An atom with equal protons and electrons is neutral; one with unequal numbers is an ion. |
| State Coulomb's Law and its formula. | F = kQ₁Q₂ / r² F = electrostatic force (N), k = 9×10⁹ N·m²/C², Q₁ and Q₂ = charges (C), r = distance (m). Positive F = repulsion; negative F = attraction. Force is inversely proportional to the square of distance. |
| If the distance between two charges is halved, what happens to the electrostatic force? | The force increases by a factor of 4. Since F ∝ 1/r², halving r substitutes (r/2)² = r²/4 into the denominator, multiplying the overall force by 4. |
| What is an electric field and how is its magnitude calculated? | A region in space where a charge experiences an electric force. E = kQ / r²; units are N/C. Field vectors point away from positive source charges and toward negative ones. Electric field strength follows an inverse square relationship with distance. |
| What are the five key properties of electric field lines? | 1) Begin on positive charges, end on negative charges. 2) Number of lines is proportional to the magnitude of the charge. 3) Closer lines = stronger field. 4) Field direction is parallel to the line at any point. 5) Field lines never cross. |
| How do you find the electrostatic force on a charge within a known electric field? | F = qE; where F is force (N), q is the test charge (C), and E is the electric field (N/C). Importantly, the electric field created by a source charge does NOT depend on the test charge — it exists regardless of whether a test charge is present. |
| Define electric potential and give its formula. | The work/energy needed to move a positive test charge from a reference point to a given point in an electric field. V = kQ / r; units are volts (V). Scalar quantity — positive for positive source charges, negative for negative ones. |
| What are equipotential lines and their three key properties? | Lines representing equal electric potential at every point along them. Properties: 1) Electric potential is the same everywhere on the line. 2) Always perpendicular to electric field lines. 3) A 3D version is called an equipotential surface. |
| What are the formulas for electric potential energy and work done by an electric field? | U = qΔV (electric potential energy, J). W = −ΔU = −qΔV (work done by the field). Work depends only on the initial and final positions, not the path taken. Moving in the direction of the field does positive work; moving against it does negative work. |
| Define potential difference and give its formula. | ΔV = V_B − V_A; the difference in electric potential between two points. Also called voltage. Work and potential energy changes depend on this value. Battery voltage is the potential difference between its terminals. |
| Explain why a negatively charged balloon clings to a neutral wall. | The balloon's neg charge repels electrons in the wall, pushing them slightly away from the balloon's side. This leaves the near side of the wall with a slight positive charge (polarization). The opposite charges attract, creating a net attractive force. |
| Does the electric field created by a source charge change if the test charge doubles? | No. E = kQ/r² depends only on the source charge Q and distance r, not on the test charge. Doubling the test charge doubles the force felt (F = qE), but the field itself is unchanged. |
| In what direction do positive charges naturally move in an electric field, and why? | From high potential to low potential. The higher the electric potential, the more electric potential energy a positive charge has — so it naturally "rolls" toward lower potential, converting potential energy into kinetic energy. |
| Why is it impossible for electric field lines to cross? | At any point in space, the electric field has only one direction. If two field lines crossed, it would imply the field simultaneously points in two different directions at the same point — a physical impossibility. |
Created by:
smurtab