Mahi Tuatahi ^🔗

1. Draw two parallel charged plates
2. Make one plate positive, and the other negative
3. Draw field lines between the two (use a ruler)
4. Describe some important features of the lines

Ngā Whāinga Ako ^🔗

1. Be able to relate $E, F$ and $q$.
2. Be able to calculate the force exerted on a charged object by an $E$ field.

Write the nga whāinga ako in your book.

Electric Fields & Forces ^🔗

• Electric fields exert a force on charged matter.
• Charged particles are simultaneously repelled by their similarly charged terminal, and attracted by their oppositely charged terminal.

$$ \begin{aligned} \text{Electric Field Strength} &= \frac{Force}{Charge} \newline E &= \frac{F}{q} \newline E &= \frac{N}{C} = NC^{-1} \end{aligned} $$

Therefore $E$ has units of $\frac{N}{C}$ ($NC^{-1}$).

Pātai ^🔗

$$ \begin{aligned} E &= \frac{F}{q} \newline \end{aligned} $$

Is electric field strength a scalar or a vector?

Whakatika ^🔗

It is a vector, because one of the components that creates it is ,force, is a vector. This means that $E$ fields have both strength (magnitude) and direction.

Ngā Pātai ^🔗

1. A small charge of $2 \times 10^{-4}C$ experiences a force of $1.5\times10^{-4}N$. Calculate the electric field strength.
2. A particle with charge $4.5 \times 10^{-5}C$ exists in an $E$ field with strength $3NC^{-1}$. Calculate the force exerted on it.

$$ \begin{aligned} & && \text{(K)} \newline & && \text{(U)} \newline & && \text{(F)} \newline & && \text{(S+S)} \end{aligned} $$

Whakatika Tahi ^🔗

A small charge of $2 \times 10^{-4}C$ experiences a force of $1.5\times10^{-4}N$. Calculate the electric field strength.

$$ \begin{aligned} E &= \frac{F}{q} \newline E &= \frac{1.5\times10^{-4}}{2\times10^{-4}} \newline E &= 0.75NC^{-1} \end{aligned} $$

Whakatika Rua ^🔗

A particle with charge $4.5 \times 10^{-5}C$ exists in an $E$ field with strength $3NC^{-1}$. Calculate the force exerted on it.

$$ \begin{aligned} E &= \frac{F}{q} \newline F &= E \times q \newline F &= 3 \times (4.5 \times 10^{-5}) = 1.35 \times 10^{-4}N \end{aligned} $$

Task/Ngohe ^🔗

• Textbook: Electric Fields Q1, Q2, Q4, Q5
  • New: pg. 192
  • Old: pg. 177
• Homework Booklet: Q3a-b

Mahi Tuatahi ^🔗

$$ \begin{aligned} & && \text{(K)} \newline & && \text{(U)} \newline & && \text{(F)} \newline & && \text{(S+S)} \end{aligned} $$

Te Whāinga Ako ^🔗

1. Be able to calculate the voltage between parallel plates

Write the date and te whāinga ako in your book

Voltage between Plates ^🔗

$$ \begin{aligned} E &= \frac{V}{d} \end{aligned} $$

Discussion / Matapaki ^🔗

$$ \begin{aligned} E &= \frac{V}{d} \end{aligned} $$

1. What is the effect of increasing/decreasing voltage on the electric field strength?
2. What is the effect of increasing/decreasing plate separation on the electric field strength?

Whakatika ^🔗

1. Increasing voltage will increase the field strength (with constant plate separation)
2. Decreasing voltage will decrease the field strength (with constant plate separation)
3. Increasing plate separation will decrease the field strength (with constant voltage)
4. Decreasing plate separation will increase the field strength (with constant voltage)

Pātai ^🔗

Whakatika ^🔗

1. Calculate the electric field strength between the two charged plates

$$ \begin{aligned} & E = \frac{V}{d} \newline & E = \frac{500}{0.02} \newline & E = 25000NC^{-1} \end{aligned} $$

2. Calculate the size of the force experienced by the charged object

$$ \begin{aligned} & F = Eq \newline & F = 25000 \times -4 \times 10^{-6} \newline & F = -0.1N \end{aligned} $$

Candles and Electric Fields ^🔗

• Collect A Candles and Electric Fields sheet.
• Come up to the front and observe the demonstration.
• Use the observations to answer Task 1-4 on your sheet.

Task/Ngohe ^🔗

• Worksheet 1: Q6a, 6bb, Q11a, 11b, 11d
• Textbook: Electric Fields Q7-8
  • New: pg. 192
  • Old: pg. 177