The Basics of Electric Fields and Capacitance

To begin, let's explore some fundamental concepts in physics. Picture two parallel metal plates, each with an area (A), positioned a small distance (d) apart. One plate carries a surplus charge (Q), while the other holds an equal but opposite charge (-Q).

When these plates are closely spaced, they create a stable electric field (E). The strength of this electric field can be quantified as follows:

Given the consistent nature of this electric field, it's relatively straightforward to compute the potential difference (ΔV) between the two plates.

This calculation is valid strictly for uniform electric fields. Knowing the electric field's magnitude allows us to substitute it into our equations.

As the charge on the plates increases, the electric field's strength also rises, leading to a higher change in potential. This direct correlation between charge and potential enables us to define a ratio known as capacitance (C), measured in Farads (F).

It's important to note that capacitance is determined solely by the capacitor's configuration; increasing the charge does not affect its capacitance.

Next, let's consider the energy stored in a capacitor. Starting from an uncharged state, moving a small charge (dQ) from one plate to the other requires no energy since the potential difference is zero. However, as charges accumulate on both plates, a potential difference arises.

The total charge Q, with its corresponding potential difference ΔV = Q/C, leads us to calculate the energy (U) involved in transferring a charge (dQ):

Typically, we focus on the potential difference rather than the charge itself, which can be measured using a voltmeter. Hence, using the relationship Q = CΔV, we derive:

To maximize energy storage, both a high capacitance and a significant potential difference are essential.

Assessing Capacitors as Phone Battery Alternatives

To determine the feasibility of replacing a phone battery with a capacitor, we first need to assess the energy capacity of a typical smartphone battery. For example, the iPhone 14 battery specifications from IFIXIT indicate it has a voltage of 3.87 volts and stores 12.68 watt-hours (Wh).

Here's a quick conversion:

Converting watt-hours to Joules requires multiplying by 3600 seconds (the number of seconds in an hour), yielding a total energy storage of approximately 13,932 Joules. To replicate this energy with a capacitor at 3.87 volts, we need a capacitance of:

This calculation results in a staggering capacitance of 1950 Farads—an impractically large value.

Now, let's visualize the physical dimensions of such a capacitor. To achieve this capacitance, we need an extensive surface area with minimal separation between the plates. However, if the plates are positioned too closely, the electric field could exceed the breakdown threshold of air (approximately 3 x 10^6 volts/meter).

Using a voltage of 3.87 volts, the minimum separation distance between the plates would be around 1.26 x 10^-6 meters, which is exceedingly small.

By applying the permittivity constant (ε₀ = 8.85 x 10^-12 F/m), we can calculate the required area to be approximately 2.77 x 10^4 m². If we were to form a square from this area, the side length would measure around 16.6 kilometers—far larger than any conventional smartphone.

Another challenge arises when using a capacitor for energy storage. As energy is drawn from the capacitor, the charge diminishes, which directly impacts the voltage across the plates. Most processors expect a consistent voltage, and if the voltage drops below a certain threshold, the device would cease to function effectively. This represents a significant drawback to using capacitors in place of traditional batteries.

Exploring Capacitor Concepts Through Video

This video provides a detailed explanation of what occurs when a parallel-plate capacitor is linked to a battery and how a dielectric material influences its functionality.

In this video, learn about a parallel plate capacitor with a capacitance of (200 mu F) connected to a (200 V) battery and the implications for energy storage.