Rail 4: Conditionals in a Scaffold - ruby-on-rails

Question

I am still learning RoR but I cant learn by following someone else's code. I have decided to implement by own app.
I have generated a scaffold and in the _form.html.erb I have this:
<div class="field">
<%= f.label :bath_accessories %><br>
<%= f.select :bath_accessories, options_for_select(["Shower", "Extractor Fan", "Lights", "Shaver", "Heat Rail"]) %><br>
</div>
When the user selects "Shower" from the above lists, I want to enable in view:
<div class="field">
<%= f.label :watts %><br>
<%= f.number_field :watts %>
</div>
I am lost where to put the if statement for: <%= f.select :bath_accessories, options_for_select(["Shower", "Extractor Fan", "Lights", "Shaver", "Heat Rail"]) %> But I did this and nothing shows:
<% if :bath_accessories[0] %>
# What to out put here with "<%= code %>?
Generated HTML Tag:
<form class="new_bathroom_accessory" id="new_bathroom_accessory" action="/bathroom_accessories" accept-charset="UTF-8" method="post"><input name="utf8" type="hidden" value="✓" /><input type="hidden" name="authenticity_token" value="r9M+Q7Np+/i68gwj65JSvV8wi4+4yb5d6tFWBHMw8k9nz1oRHGzh7AZHOTFvlaiS2lmqTch356vVYNlh7Urifw==" />
<div class="field">
<label for="bathroom_accessory_bath_accessories">Bath accessories</label><br>
<select name="bathroom_accessory[bath_accessories]" id="bathroom_accessory_bath_accessories"><option value="Shower">Shower</option>
<option value="Extractor Fan">Extractor Fan</option>
<option value="Lights">Lights</option>
<option value="Shaver">Shaver</option>
<option value="Heat Rail">Heat Rail</option></select><br>
</div>
<div class="field">
<label for="bathroom_accessory_watts">Watts</label><br>
<input type="number" name="bathroom_accessory[watts]" id="bathroom_accessory_watts" />
</div>
<div class="field">
<label for="bathroom_accessory_volts">Volts</label><br>
<input type="number" name="bathroom_accessory[volts]" id="bathroom_accessory_volts" />
</div>
<div class="actions">
<input type="submit" name="commit" value="Create Bathroom accessory" />
</div>
</form>

Answer 1

By adding an id to particular <div>,you can control that <div> as per user selection.
<div class="field" id="shower_id">
<%= f.label :watts %><br>
<%= f.number_field :watts %>
</div>
And you need JavaScript or JQuery code like this
$('#bathroom_accessory_bath_accessories').on('change',function(){
if( $(this).val()==="Shower"){
$("#shower_id").show()
}
else{
$("#shower_id").hide()
}
});
DEMO