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Physics 19
| Question | Answer |
|---|---|
| What is electric potential (Va)? | The electric potential energy (EPE) per unit charge (q) at a point: Va = EPEa / q |
| What is the formula for electric potential due to a point charge? | V = kq/r, where zero potential is at infinity |
| What is the SI unit of electric potential? | The volt (V), where 1 V = 1 J/C |
| What is the work done by electric forces on a charge? | W = -q(Vf - Vi), since electric force is conservative and work depends only on initial and final positions |
| What is an electron volt (eV)? | The energy gained by an electron accelerated through 1 volt of potential difference; 1 eV = 1.6 × 10⁻¹⁹ J |
| What is the electric potential energy of a pair of point charges? | EPE = kq₁q₂/r |
| What are equipotential lines? | Lines connecting points of equal electric potential; they are always perpendicular to electric field lines |
| What is capacitance and its unit? | The ability of a capacitor to store charge; Q = CV, measured in Farads (F), where 1 F = 1 C/V |
| What is the formula for capacitance of a parallel plate capacitor? | C = κε₀(A/d), where κ is the dielectric constant, A is plate area, and d is plate separation |
| What are the three formulas for energy stored in a capacitor? | Energy = ½QV = ½CV² = ½Q²/C |
| What is a dielectric and what is its minimum value? | An insulating material placed between capacitor plates; its constant κ has a minimum value of 1 (dry air) |
| How do you find total EPE of a system of charges? | Sum the EPE of each unique pair — do not sum per individual charge or you'll double the energy |
| Why is electric force considered a conservative force? | Because the work done by the electric force depends only on the initial and final positions, not the path taken between them |
| If a charge moves along an equipotential surface, how much work does the electric field do? | Zero, because there is no change in electric potential (Vf = Vi), so W = -q(Vf - Vi) = 0 |
| What happens to the electric potential energy when two like charges are brought closer together? | It increases, because work must be done against the repulsive force between them |
| What is the relationship between the direction of the electric field and the direction of increasing potential? | The electric field points from high potential to low potential; E = -ΔV/Δs |
| Why does W1 equal zero when bringing the first charge in from infinity? | Because there is no existing electric field yet, so there is no potential acting on the first charge — both q1V1i and q1Vf cancel out |
| Why does increasing the distance between capacitor plates decrease capacitance? | Because capacitance C = κε₀A/d — distance is in the denominator, so larger separation means less ability to store charge |
| What is the physical role of a dielectric in a capacitor? | It prevents the plates from touching, and by having κ > 1, it increases the capacitance compared to air or a vacuum |
| Why can a capacitor release energy more dramatically than it stores it? | Energy is stored gradually over time, but can be discharged nearly instantaneously through a closed circuit, releasing all stored energy at once |
| What does it mean physically when electric potential is zero at infinity? | It is an arbitrary reference point chosen for convenience — it means a charge infinitely far from a source charge has no electric potential energy relative to it |
| How does the sign of a point charge affect the electric potential around it? | A positive charge creates positive potential in the surrounding space, while a negative charge creates negative potential — since V = kq/r, the sign of q determines the sign of V |
| Tip About Capacitor Modifications | If the change is made after the battery is disconnected, the charge will stay the same (C) and if the modification is made with the battery still connected, the voltage (V) will stay the same. |
| Complete Lecture Problem 1 | -- |
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| Complete Lecture Problem 7 | -- |
| Complete Recitation Problem 1 | -- |
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| Complete Homework Problem 3 | -- |
| Complete Homework Problem 4 | -- |
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| Complete Homework Problem 10 | -- |
Created by:
smurtab