As commented above, the two sentences don't have the same meaning. In order to understand what the passive voice is, you need to understand the followings.
- There should be an agent (that performs an action) and patient (that receives an action). The definition of patient is as follows:
the semantic role of a noun phrase denoting something that is affected
or acted upon by the action of a verb.
In the passive voice, the agent is almost always placed after the preposition by. The reason the preposition to is used in your example is "known" is not a past participle, but an adjective meaning:
recognized, familiar, or within the scope of knowledge.
In "I know him", "I" is an agent and "him" is a patient (object). However, "He is known to me", "He" is not an patient in a sense that it doesn't receive any action. "He" is just a subject which is described by the adjective "known". If you replace "known" with "familiar", it would be easier to understand.
He is familiar to me.
It is not a passive voice sentence.
- Not all the past participles are used in the passive voice. Sometimes they function as an adjective. There is no hard-and-fast rule, but for example,
He was surprised at the news.
This sentence is not in the passive voice. "Surprised" is just an adjective meaning feeling or showing surprise. "At the news" is a prepositional phrase that complements the adjective.
The news surprised him.
is an active voice. The passive voice of the above sentence should be
He was surprised by the news. (He is the patient, the news is the agent)
The below sentence is in the passive voice of "A baseball broke the window".
The window was broken by a baseball.
However, the below sentence is not in the passive voice. There is no agent.
The window was broken and a strong wind came through it (the broken
- To know is classified as a stative verb rather than a dynamic (action) verb. The main characteristics of the stative verb are:
(1) you don't make a progressive sentence with it (there are some
(2) Constructing a passive voice of the stative verbs don't work very
well and the passive voice sentences don't sound natural.
?He is known by me (I know him). ?A car is had by me (I have a car). ?He is believed by me (I believe him).
This link has a list of stative verbs. Learning what they are and how they typically work is very important.
Conclusion: "He is known to me" is not in the passive voice. "Known" is an adjective, not a past participle. If you contrast your example with "He is well-known to me", it becomes clearer. It is not the passive voice of "I know him well".