quiz 2: capacitors and dielectrics

An air-filled parallel-plate capacitor has a capacitance of 1 pF. The plate separation is then doubled and a wax dielectric is inserted, completely filling the space between the plates. As a result, the capacitance becomes 2 pF. The dielectric constant of the wax is: 

• 0.25 
• 0.50 
• 2.0
• 4.0

A dielectric slab is slowly inserted between the plates of a parallel plate capacitor while the capacitor is connected to a battery.  As it is being inserted:

• the capacitance and the charge on the plate increase but the potential difference between the plates remains the same
• the capacitance and the charge on the positive plate decrease but the potential difference between the plates remains the same
• the potential difference between the plates increases, the charge on the positive plate decreases, and the capacitance remains the same
• the capacitance, the potential difference between the plates, the charge on the positive plate all decrease

During charging a capacitor through a resistor

• the current in the circuit increases linearly with time

• the current in the circuit decreases linearly with time

• the current in the circuit increases exponentially with time

• the current in the circuit decreases exponentially with time

How is the capacitance (C) of a parallel-plate capacitor affected by the charge on the plates ?

• C depend on the charge on the plates

• C is vanished when there are plates

• C does not depend on the charge on the plates

• C is accumulated on one side only

A dielectric slab is slowly inserted between the plates of a parallel plate capacitor while the capacitor is connected to a battery.  As it is being inserted:

• the capacitance and the charge on the plate increase but the potential difference between the plates remains the same
• the capacitance and the charge on the positive plate decrease but the potential difference between the plates remains the same
• the potential difference between the plates increases, the charge on the positive plate decreases, and the capacitance remains the same
• the capacitance, the potential difference between the plates, the charge on the positive plate all decrease

Tags

NGSS.HS-PS3-5

When a 4 V battery is connected to a capacitor, what is the voltage across the capacitor after a long period of time?

• 0.0 V

• 2.0 V

• 4.0 V

• 3.0 V

The following diagram features 4 capacitors, each of capacitance 3nF, connected to a 50 V battery. The capacitance of the equivalent capacitor is equal to:

• 2 nF
• 3 nF
• 5 nF
• 7.5 nF

In the below figure for capacitors connected in parallel, what is the correct statement and formula ?

• The Total charge will be the sum of the charges in each of three capacitors QT=Q1+Q2+Q3

• Charge in each capacitor is the same QT=Q1=Q2=Q3

• Charge in each capacitor is different but current in each capacitor are the same

• The total charge will be QT=Q1- Q2 - Q3

In the circuit to the right, if C= 10μF, R=3.3KΩ, then the time constant (τ) for the circuit is:

• τ = 0.064s
• τ = 0.021s
• τ = 0.033s
• τ = 0.042s

In the circuit to the right, if C= 20μF, R=15KΩ, then the time needed for the capacitor to be fully charged is:

• 0.8s
• 1.0s
• 1.3s
• 1.5s